Modern slavery in supply chains: toward a theoretically based research agenda

Research on modern slavery (MS) in supply chains (SCs) is recently proliferating (e.g. Crane et al., 2022; Emberson et al., 2022; Flynn and Walker, 2021; Pinnington et al., 2023; Schaper and Pollach, 2021; Sokat and Altay, 2022; Stevenson, 2022; Stringer and Michailova, 2018). Despite the recent increased attention, research on MS in SCs (hereafter referred to as MS) remains relatively limited (Caruana et al., 2021; Han et al., 2022; Mehmood et al., 2023). This is untenable because MS is an important social and business concern, posing risks of litigation, reputation damage, consumer boycotts and financial losses (Monciardini et al., 2021; Sokat and Altay, 2022). Hence, this study used six organizational theories at the environmental, firm and transaction levels to develop a multitheoretical framework and research agenda for MS.

This study was conducted to bridge the following four gaps. First, literature reviews on MS conducted by Han et al. (2022), Mehmood et al. (2023) and Strand et al. (2023) reported that despite the rapid increase in MS publications, there remains a dearth of theory-driven research, and in-depth theoretical understanding of MS is lacking. Second, as the literature in a field expands, research must shift focus from exploratory to theory-driven analyses (Edmondson and McManus, 2007). Most extant MS studies explicitly state that they are exploratory (Liu et al., 2022; Monciardini et al., 2021; Robb and Michailova, 2022; Stevenson and Cole, 2018). Other studies are also predominantly descriptive and exploratory in nature, examining MS using news reports (Sokat and Altay, 2022; Stevenson, 2022), interview data (Lafargue et al., 2022; Simpson et al., 2021), case studies (Crane et al., 2022) and secondary data such as firms’ MS statements (Meehan and Pinnington, 2021; Schaper and Pollach, 2021). While these studies significantly help understand MS, they lack theoretical analyses. Deficiency of theory use as literature grows can lead to intellectual stagnation and hinder knowledge development in a field (Moller and Halinen, 2022). Third, the “theoretical toolbox” approach has been used to develop research agendas for strategic sourcing (Shook et al., 2009) and pandemics and SCs (Craighead et al., 2020), among others. However, a systematically applied organizational theory to develop a theoretical toolbox for MS research is lacking. Fourth, research on social concerns in SCs has evaded MS (Nakamba et al., 2017; Stevenson and Cole, 2018), which is complex, criminal and illicit (Crane et al., 2022), unlike other social concerns. MS requires specific and targeted research (Stevenson and Cole, 2018).

Therefore, this study developed a multitheoretical framework and research agenda for guiding future MS research. The study proposes research directions (RDs) for MS based on institutional, stakeholder, resource-based, resource dependence, principal agent and transaction cost economics (TCE) theories. This study poses three research questions:

The unit of analysis is the focal buying firm, i.e. large multinational corporation (MNC), and the context is its global SC (GSC).

This study contributes to the existing literature in the following ways. First, it bridges the literature gap regarding MS (Caruana et al., 2021; Han et al., 2022). Second, it responds to calls for theory-based MS research (Caruana et al., 2021; Crane et al., 2022; Strand et al., 2023). Third, using a multitheoretical framework for MS, this study facilitates a multifaceted analysis consistent with MS, a complex and multilevel governance problem in GSCs (Burmester et al., 2019; Meehan and Pinnington, 2021).

The remainder of this paper is organized as follows. Section 2 presents the background, definitions, overview and examples of MS. Section 3 presents the study’s methodological approach. Section 4 presents the literature review findings. Section 5 is the major portion of the paper, it applies the selected theories to MS and draws on the themes that emerged from the relevant literature reviewed to develop a theoretical framework and research agenda for MS, comprising 20 RDs. The discussion follows in Section 6. The research, practical and policy implications of the study are presented in Section 7. The limitations of the study are outlined in Section 8. Finally, the paper concludes by inviting research on MS using the proposed RDs and theories.

The International Labor Organization (ILO) identifies two primary MS categories: forced labor and forced marriage [International Labour Organization (ILO) et al., 2022]. This study solely considers forced labor. The terms “MS” and “forced labor” are frequently used interchangeably (Robb and Michailova, 2022). This study focuses on MS in the SCs of corporations and uses the definition “the exploitation of a person who is deprived of individual liberty anywhere along the supply chain, from raw material extraction to the final customer, for the purpose of service provision or production” (Gold et al., 2015, p. 487). This definition is suitable for this study because it solely focuses on MS in SCs and excludes other forms of slavery. Table 1 presents some of the numerous definitions of MS in the literature. Based on these definitions, MS is characterized by forced, bonded, trafficked and child labor; labor exploitation, hazardous working conditions, human and labor rights violations, exploitative recruitment practices, dehumanization of workers and restricted or loss of freedom of movement [Caspersz et al., 2022; Flynn and Walker, 2021; International Labour Organization (ILO) et al., 2022; Strand et al., 2023]. Nevertheless, no single specific definition clarifies its scope and different forms, causing possible impediments to tackling MS because “identifying instances of modern slavery remains difficult given the lack of a hard and unequivocal definition” (Caspersz et al., 2022, p. 181).

Historical slavery was centered on the transatlantic slave trade, and slaveholders had legal ownership of slaves (Strand et al., 2023). Conversely, enslaved people are not owned in contemporary forms of slavery (Strand et al., 2023). The phrase “modern slavery” gained prominence recently (Stringer and Michailova, 2018) to clarify and elucidate contemporary forms of exploitation. Approximately 28 million people are in forced labor in the private sector worldwide, and services, manufacturing, construction and agriculture are the most affected sectors [International Labour Organization (ILO) et al., 2022]. The ILO estimates that MS generates US$150bn in illegal profits annually [International Labour Organization (ILO), 2024]. Across regions, Asia Pacific, Europe, Central Asia, Africa and the Americas have the highest MS prevalence [International Labour Organization (ILO) et al., 2022].

Several international legislations and initiatives prohibit MS. The United Nations (UN) outlawed slavery through the 1926 Slavery Convention [Office of the High Commissioner for Human Rights (OHCHR), 1926]. The 1956 UN Supplementary Convention on the Abolition of Slavery extended the original definition of slavery to include all forms of slavery, the slave trade and “institutions and practices similar to slavery” [Office of the High Commissioner for Human Rights (OHCHR), 1956, p. 1). Article Four of the Universal Declaration of Human Rights of 1948 prohibits slavery in all forms [United Nations (UN), 1948]. In 2000, the UN adopted the Protocol to Prevent, Suppress and Punish Trafficking, especially Women and Children, also referred to as the “UN Trafficking Protocol” [Office of the High Commissioner for Human Rights (OHCHR), 2000]. The updated Protocol of 2014 of the Forced Labor Convention of 1930 prohibits forced labor (ILO, 2014). The UN sustainable development goals (SDGs), specifically UN Target SDG 8.7, aim to eradicate MS [United Nations (UN), 2015]. Regulators from various jurisdictions have enacted legislation to combat MS, including the UK Modern Slavery Act [United Kingdom (UK) Government, 2015], Australia Modern Slavery Act (Australia Government, 2018), French Duty of Vigilance Law [European Trade Institute (ETUI), 2017], Dutch Child Labor Due Diligence Act (Amfori, 2019) and California Transparency in Supply Chains Act (State of California, 2010), among others. As more MS laws are enacted, corporations that are found to have MS in their SCs will face litigation risks.

The literature reports numerous cases of MS. In 2013, Rana Plaza, a Bangladeshi commercial building that housed five garment factories and supplied to major European and US MNCs, brands and retailers, collapsed, killing 1,134 and injuring 2,500 workers (Frenkel et al., 2022). Unsafe working conditions, worker rights violations and worker exploitation concerns were observed in the factories (Frenkel et al., 2022). This disaster highlighted the extremely exploitative labor practices in the global garment SC, of which Bangladesh is a significant supplier (Frenkel et al., 2022). Recently, a case study of workers in Bangladeshi clothing factories linked to global clothing SCs found evidence of workers’ rights violations, which worsened during the coronavirus disease 2019 (COVID-19) pandemic (Uddin et al., 2023). The Thailand fishing industry faced an MS crisis characterized by severe labor abuse of primarily migrant workers (Stringer et al., 2022; Wilhelm et al., 2020). This industry is a significant segment of the global seafood SCs, providing for some of the largest MNCs, retailers and seafood brands worldwide (Stringer et al., 2022). Stringer et al. (2016) found evidence of forced labor in foreign vessels fishing in New Zealand waters, including deceptive recruitment, debt bondage, labor exploitation, dangerous work, low or no wage payment and confiscation of documents such as passports.

The Ghanaian cocoa industry – a segment of global cocoa SCs – had labor exploitation and child labor and trafficking (LeBaron and Gore, 2020). The world’s leading chocolate companies that source cocoa from Ghana have faced child slavery lawsuits in the USA [Business and Human Rights (BHR), 2023]. Marshall et al. (2022) investigated sandstone global value chains linked to India’s Rajasthan sandstone quarries and found evidence of child and bonded labor, meager wages and significant worker health and safety concerns. GSCs of the Democratic Republic of Congo (DRC)-mined cobalt are associated with child labor, dangerous working conditions and human rights abuse (Sovacool, 2021). MS was identified in the DRC–UK cobalt SC (McQuilken et al., 2022) and the Brazil–UK beef and timber SCs (Emberson et al., 2022). Furthermore, prior studies and reports suggest MS risks in SCs of various products, including electronics, footwear, shrimp, tea and diamonds [e.g. International Labour Organization (ILO) et al., 2022; LeBaron, 2021].

Considering the nascent MS literature and lack of theory use, this study aimed to review literature review studies on SC social sustainability to identify the typically used theories in examining social concerns representing or associated with MS and select six among them to use in this study. Furthermore, the study aimed to systematically review relevant literature on social concerns in SCs and synthesize the findings thematically. Then the study aimed to build on these theories and thematic findings to develop a research agenda and directions for future studies focused on MS.

This study analyzed relevant literature review studies to identify and select six theories to use and conducted systematic literature review (SLR) of relevant studies using the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines (Liberati et al., 2009; Page et al., 2021). Drawing on the selected theories and identified themes from SLR, the study develops a multitheoretical framework and future RDs for MS. Figure 1 illustrates the primary steps followed and the research questions in this study. The primary steps are detailed in the following sections.

Literature reviews can be used as a research method to compile and summarize available information in a field and facilitate the evaluation of combined or cumulative evidence (Snyder, 2019). Extant literature reviews on (socially) sustainable supply chain management (SSSCM/SSCM) and corporate social responsibility (CSR) have identified the most frequently used theories for studying social concerns in SCs. To identify the theories to be used, this study reviews extant SSSCM/SSCM and CSR literature to gain a high-level summary of the primary theories used to study SCs’ social concerns. Social concerns in SCs, such as forced or child labor, labor exploitation and human or labor rights violations, are constituent elements of MS (Stringer et al., 2022). These have been studied in the SSSCM/SSCM and CSR contexts without necessarily being labeled “modern slavery.” Therefore, these previously used theories can be extended to explicitly study MS. Organizational theory is an interdisciplinary body of principles used to study and explain organizational behaviors, operations and phenomena (McKinley, 2010). Although organizational theory has been applied to green SC management (Sarkis et al., 2011) and GSCs (Connelly et al., 2013) to identify future RDs, its application to MS has been neglected. This study follows the approach of Craighead et al. (2020) and Sarkis et al. (2011) in using organizational theory to develop a research agenda for MS.

A systematic review process was used to identify, select and analyze relevant review studies (Tranfield et al., 2003). This process comprised three steps. The first step was to identify the search terms to be used as follows: “social sustainability” OR “socially sustainable” OR “corporate social responsibility” OR “socially responsible sourcing” AND “supply chain” OR “value chain” AND “literature review” OR “systematic literature review.” Subsequently, searches were conducted in several academic databases, including Web of Science, Scopus, Google Scholar, ScienceDirect, Emerald Insight and JSTOR. Publications obtained after this search were individually screened to identify those that summarized the predominantly used theories regarding social concerns in SCs. The inclusion criterion was solely peer-reviewed journal studies, which were literature reviews on social sustainability or social issues in SCs. Book chapters, conference studies and nonpeer-reviewed studies were excluded. Finally, five literature review studies were deemed suitable for this study’s aims because they reviewed the typically used theories to study social issues in SCs representative of MS, as presented in Table 3 in subsection 4.1.

This study identified key themes emerging from the extant literature that examined social concerns in SCs using the selected theories. To review relevant literature, SLR was conducted following the PRISMA guidelines. A flow diagram of this study using PRISMA guidelines is illustrated in Figure 2. Computer-assisted searches were conducted in several academic databases – Web of Science, Scopus, Google Scholar, ScienceDirect, Emerald Insight and JSTOR.

The main search terms used were “social sustainability,” “supply chain” and “theory.” Table 2 presents the synonyms and related terms for these keywords. All search terms were combined with “AND” and “OR” in the search queries, and the terms were used in various combinations to obtain all possible studies. The search yielded 1,936 studies, of which 1,822 were identified as duplicate, irrelevant and nonpeer-reviewed studies such as book chapters and conference papers. Subsequently, the remaining 114 studies were screened by title and abstract to identify only those relevant to this study.

Studies were included if they focused on social sustainability or responsibility in SCs; mentioned social issues such as forced, child or bonded labor, labor exploitation, human or labor rights violations and worker health and safety; and used (at least) one of the theories used in this study. An article had to state explicitly that a specific theory was used, mention the theory several times or state that it drew insights from the theory for it to be included. Studies were excluded if they did not directly mention social sustainability in SCs or any of the social issues, did not explicitly use theory or focused on other types of sustainability, such as environmental sustainability. Although the criteria excluded environmental or green sustainability studies, Sarkis et al. (2011) were included because of their high relevance to this study. After the screening phase in which the inclusion and exclusion criteria were applied, 35 studies were excluded. Next, a comprehensive analysis was conducted on each of the remaining 79 studies to confirm their eligibility, leading to the exclusion of 34 studies because they merely mentioned social concerns without explicitly analyzing them using the theory, or their findings did not provide valuable and pertinent insights to guide future research for MS. The remaining 45 studies were selected for review and thematic analysis. The main themes that emerged from the selected studies are presented in subsection 4.2. A separate search was conducted using the keyword “modern slavery” to identify MS studies that used the theories selected for this study.

Table 3 presents the selected literature review studies that identified the typically used theories (column four) to study social concerns in SCs representative of MS (column three). This study chose to use institutional, stakeholder, resource-based, resource dependence, principal-agent and TCEs theories. These theories are suitable for this study because they have been used to examine social concerns in SCs that are constituent elements of MS (Stringer et al., 2022). Furthermore, in studying SC-related problems, it is logical to use theories previously validated and proven in prior comparable studies (Halldórsson et al., 2015). In addition, the selected theories are recommended as suitable for future MS research (Han et al., 2022; Mehmood et al., 2023; Stevenson and Cole, 2018). This analysis addressed the first research question. These six theories were used to develop a research agenda and direction for MS, as presented in Section 5. For completeness, literature review studies that identified dominant theories within the broader SSCM field were also reviewed and presented in Table 3 (Carter et al., 2020; Koberg and Longoni, 2019; Touboulic and Walker, 2015).

Relevant studies were systematically reviewed and thematically analyzed, and the main themes that emerged from the literature review were categorized according to the theories used, as presented in Table 4, to gain insights into potential thematic directions for future research focused on MS.

This analysis addressed the second research question. The themes identified in relevant studies were used to develop future RDs focused on MS, as presented in Section 5.

Figure 3 presents a multitheoretical framework, and Table 5 presents 20 theory-driven RDs for MS based on six theories, focusing on the environmental, firm and transaction levels of analysis. Table 5 lists theories, disciplines, fundamental premises and potential RDs. The following subsections focus on each of the theories. Each subsection presents a brief overview of the theory, its suitability for MS research, analysis of relevant literature and RDs for MS using the theory.

Institutional theory (IT) posits that firms are embedded in and influenced by the institutional contexts within which they operate (Scott, 1995). Organizations face coercive, normative and mimetic institutional pressure from their environments (DiMaggio and Powell, 1983). Oliver (1991) suggested five organizational responses to institutional pressures: defiance, avoidance, compromise, acquiescence and manipulation. To attain and maintain legitimacy, organizations must comply with the norms, values and standards of their institutional environments (March and Olsen, 1983). IT is a typically used theory in MS research (Diab, 2022; Flynn, 2020; Flynn and Walker, 2021; Liu et al., 2022; Stevenson and Cole, 2018). This is because it facilitates examining MS legislation, corporate obligations and responses and the effect of institutional settings on MS (Strand et al., 2023). Nevertheless, IT can be further applied to advance knowledge on MS by examining how institutional quality may influence the effectiveness and enforcement of MS laws (Mehmood et al., 2023). As MS concerns are becoming increasingly prominent in business and society, corporations face rising institutional pressures to address these concerns to maintain their social legitimacy (Flynn and Walker, 2021).

IT has been used in SSCM (Nath et al., 2020; Paulraj et al., 2017; Silvestre et al., 2020; Wu and Jia, 2018), SSSCM (Kauppi and Hannibal, 2017; Kelling et al., 2021; Mani and Gunasekaran, 2018; Moxham and Kauppi, 2014) and CSR (Schultz and Wehmeier, 2010). Insights from these studies help to develop RDs focused on MS. IT can be used in four RDs for MS, as presented in Table 5 (RD1-4) and Figure 3. An analysis of the selected literature and directions for future MS research follow.

The SSSCM literature shows that regulatory compliance pressure from legal authorities can force corporations to behave in a socially responsible manner in their SCs (Mani and Gunasekaran, 2018). This implies that, in the context of MS, laws can pressure MNCs to eliminate MS from their SCs. As outlined earlier, numerous legislations have been enacted to combat MS. Focal firms face increasing legislative pressure to address MS (Monciardini et al., 2021). Despite existing legislations, MS persists in MNCs’ GSCs (Ishaya et al., 2024; Stringer and Michailova, 2018), suggesting that legal and regulatory institutions are not sufficient in preventing MS. Empirical research is required on how institutional pressures from governments and regulatory bodies in home and host countries and international regulatory institutions such as the UN and the ILO can pressurize MNCs to adopt MS-free practices in their SCs. Kauppi and Luzzini (2021) developed a scale to measure institutional pressures for sustainability in the SC context. Thus, future MS studies can investigate and measure the impact of institutional pressures on MNCs’ adoption of MS-free practices in their SCs.

Prior SSCM research has identified numerous sources of institutional pressure for sustainability in SCs, including external stakeholders, such as nongovernmental organizations (NGOs), social activists, local governments and the media (Mani and Gunasekaran, 2018). Due to complex GSCs and the hidden nature of MS (Pinnington et al., 2023), solely coercive pressure from governments or regulatory institutions may not sufficiently influence the adoption of MS-free practices in MNCs’ SCs. The effectiveness of MS regulations may be limited by the complexity and opacity of GSCs, the power MNCs exert in their SCs, the challenges MNCs present to transnational labor governance and the limitations of nation-states in monitoring labor standards in their countries (Burmester et al., 2019; Stringer and Michailova, 2018). There is limited knowledge regarding the various sources of institutional pressure that influence MS-free practices in SCs. The SSSCM literature also suggests that third-party voluntary certifications can directly and indirectly exert institutional pressure on MNCs to improve social sustainability of their SCs (Kauppi and Hannibal, 2017). Extant MS research suggests that because of the complexity of MS in SCs, public legislation and private initiatives are both required to tackle this issue more effectively (LeBaron and Rühmkorf, 2019). Future studies can empirically investigate how combined direct and indirect institutional pressures from different actors can generate substantial institutional pressures for the adoption of MS-free practices in MNCs’ SCs.

Prior SSCM studies indicate that response to institutional pressure depends on corporate motives and performance outcomes of sustainable practices; corporations respond differently to institutional pressures for SSCs depending on their instrumental, relational and moral motivations; and whether such practices can improve their financial performance (Paulraj et al., 2017). This implies the importance of understanding the relationship between institutional pressures for adopting MS-free practices, corporate motives and the subsequent performance outcomes. There is a need to understand how firms’ motives and potential performance outcomes of MS-free practices shape their response to institutional pressures to address MS.

Moreover, institutional pressures for sustainability can cause symbolic rather than substantive adoption of sustainability standards, leading to corrupt SC practices (Silvestre et al., 2020). Applying this to the context of MS implies that institutional pressures may not result in tangible changes or improvements for addressing MS. Several MS studies show that some firms’ responses to the UK MS Act (2015) are symbolic and ineffective in addressing MS (Flynn and Walker, 2021; Monciardini et al., 2021). Prior studies examined firms’ responses to MS legislation in construction (Liu et al., 2022), food and tobacco industries (Monciardini et al., 2021) and those listed on the UK stock exchange (Flynn and Walker, 2021). Nonetheless, future studies must evaluate institutional pressures and corporate responses, specifically how such pressures may lead to symbolic responses in various industries.

Collectively, these SSSCM/SSCM studies can inform and guide future research on MS, a complex, significant and urgent SC concern. There is a need to analyze and understand the sources of coercive, normative and mimetic pressures faced by MNCs to address MS and the effectiveness of these institutional pressures. The cause-and-effect relationship between institutional pressures and the adoption of MS-free practices is critical in highlighting how institutions can be used to influence MNCs to implement anti-MS policies and practices in their businesses and SCs. Studies can investigate and measure direct and indirect institutional pressures for MS-free SCs across different products, services and industries and analyze the firms’ responses to these pressures (RD1). This RD can catalyze policy interventions to address MS through more effective and enforceable MS laws. The RD can also generate knowledge that can help NGOs, activists, customers and the media to gain a deeper and nuanced understanding of how they can more effectively exert pressures on MNCs to address MS. This RD can help understanding how MNCs could be more influenced by their surrounding institutions and anti-MS laws, to eradicate MS in their SCs.

The SSSCM literature shows that institutional voids, characterized by absent, weak or poorly functioning institutions, are a common concern in emerging or developing economies where most low-tier SCs are located, hindering social sustainability in the SCs of MNCs (Kelling et al., 2021; Silvestre, 2015). The lack of or ineffective law enforcement, corruption and opportunistic behavior can reduce SC sustainability (Silvestre et al., 2018, 2020). Regarding MS, empirical research is required on how institutional voids can affect MNCs’ abilities to implement anti-MS policies and practices in their SCs. A few MS studies have already explored this path and have shown that complex multitiered GSCs that span diverse institutional contexts, including those characterized by institutional voids, present challenges for tackling MS (e.g. Diab, 2022). There is a need to comprehensively examine the nature of institutional voids in emerging economies and their effect on MS in GSCs. Studies show that institutional voids can cause conflicting institutional logic and supplier decoupling from sustainability compliance (Kelling et al., 2021; Nath et al., 2020). The lack of, weak, or uneven law enforcement by local governments can cause conflicting institutional logics that allow low-tier suppliers to engage in corruption and decouple the implementation of sustainable practices in SCs using various decoupling strategies, such as concealment, misleading presentation and symbolic adoption (Nath et al., 2020). Suppliers in inefficient institutional environments intentionally hide nonconforming activities such as the use of forced and child labor (Huq et al., 2014). These SSSCM studies provide valuable insights for future research explicitly focused on MS. As MS persists in low-tier SCs, it is necessary to conduct in-depth investigation of how suppliers may decouple the implementation of MS-free practices in challenging institutional contexts characterized by weak or undeveloped formal institutions.

Considered together, these SSSCM studies provide directions for future MS-focused research on how institutional voids can affect the adoption and implementation of MS-free practices in SCs. An in-depth understanding of the institutional voids confronting MNCs is urgently required, to enable them to successfully tackle MS in their GSCs. In-depth empirical research must analyze how high institutional voids affect the adoption, implementation and monitoring of MS-free practices in GSCs (RD2) to provide actionable knowledge for MNCs.

Schultz and Wehmeier (2010) examine the institutionalization of CSR practices at the macro-, meso- and micro-levels. This suggests that, regarding MS, corporations must institutionalize anti-MS laws and policies in their organizational cultures and practices across all levels. Research must examine how to institutionalize anti-MS practices at the macro-, meso- and micro-levels within organizations and in SCs in contexts with high institutional voids. Future MS studies may conduct multilevel analyses of the institutionalization and diffusion (Deephouse and Suchman, 2008) of anti-MS laws, standards and practices. If MS laws are not established as institutional norms in organizations and their cultures, this can hinder their abilities to tackle MS. Lack of institutionalization and dissemination of MS laws across all levels of the organization and SCs can cause ambiguity regarding the laws and their interpretation and implementation, creating challenges in addressing MS. Extant SSCM research has examined micro-foundations of SC sustainability practices relating to individual behaviors and choices (Dias et al., 2023). There is a lack of research on the micro-foundations of MS-free SC practices, focusing on individual-level behaviors, motivations and choices (e.g. employees and managers) and how these aggregate and affect the organizational or macro-level performance on MS. Studies must examine the institutionalization of MS-free practices at different firm levels. They can investigate the multilevel (micro–meso–macro) and micro-foundations (individual-level) of the institutionalization of MS-free practices in MNCs and their SCs (RD3). Findings from these studies can help MNCs institutionalize MS laws and practices in their organizations and SCs. Such studies can generate knowledge MNCs can use to institutionalize, disseminate and communicate their anti-MS values and principles at different organizational levels. Knowledge of the micro-foundations of MS-free SC practices can help MNCs understand how individuals’ actions and behavior can enhance or diminish sustainability outcomes (i.e. MS-free practices) at the organizational level. MNC executives can also use this knowledge to better understand ways to operationalize MS-free standards and obligations effectively, and motivate their employees and SC partners to adopt slavery-free standards and values.

The SSSCM literature shows that low-tier suppliers can resist socially sustainable practices (Nath et al., 2020). Explicitly for MS, there is a literature gap regarding organizational resistance to institutional pressures to adopt MS-free practices in SCs of various products where MS persists despite the MS legislation and institutional pressures. According to IT, acquiescence to institutional pressures increases organizational legitimacy (Oliver, 1991). Thus, future empirical research must explore how institutional resistance or a lack of acquiescence to institutional pressures may impact organizational legitimacy of MNCs from the perspectives of their stakeholders. Lafargue et al. (2022) suggest potential institutional rejection regarding MS, stating that, to a certain extent, the chocolate industry has rejected legislative coercive and consumer normative pressures to address child labor in its SCs, demonstrating how firms’ profit objectives may overshadow sustainability considerations and institutional pressures. There is limited understanding regarding how MNCs’ active (or passive) resistance to institutional pressures regarding MS practices manifests, and how this resistance could be addressed.

Future research must investigate the effect of institutional pressures on adopting MS-free practices in SCs of various products and industries, and examine MNCs’ resistance to such institutional pressures. Gold et al. (2015) encourage researchers to “investigate why and how slave-holders can continuously resist mimetic, normative and coercive isomorphic pressures towards more legitimate forms of business” (p. 491) to enable SC practitioners to “see more clearly which actions to take (also in collaboration with other non-economic actors) to weaken this resistance, with the ultimate aim of making their supply chains slavery free” (p. 492). Drawing insights from these studies, future empirical studies can explore institutional resistance or rejection of adopting MS-free practices in SCs and investigate the strategies MNCs may use in response to institutional pressures to tackle MS (RD4). This line of inquiry can shed more light on how to address institutional resistance, exert adequate institutional pressure on MNCs and influence them to adopt MS-free practices in their SCs.

Freeman (1984) defines a stakeholder as “any group or individual who can affect or is affected by the achievement of an organization’s objectives” (p. 46). Firms’ stakeholders can be categorized as direct and indirect (Freeman, 1984) or primary and secondary (Key, 1999). Mitchell et al. (1997) advanced the theory of stakeholder identification and salience based on three qualities: power, legitimacy and urgency. Mitchell et al. (1997) identified seven types of stakeholders based on their characteristics: definitive, dominant, dangerous, demanding, dependent, discretionary and dormant. Firms must identify and prioritize the most significant stakeholders influencing their operations and formulate strategies to respond to their needs (Freeman, 1984; Mitchell et al., 1997).

Few MS studies have used stakeholder theory (ST) (Liu et al., 2022; Robb and Michailova, 2022; Sokat and Altay, 2022). Although MS is gaining increasing attention from MNCs’ stakeholders such as policymakers, governments, NGOs, consumers and activists, only a few studies have used ST to examine corporations’ stakeholders (Han et al., 2022). Strand et al. (2023) argued that “there are a range of actors and stakeholders found within and outside the supply chain. They all play a role in either preventing, facilitating or experiencing the occurrence of MS and forced labor within supply chains. Stakeholders include the focal firm, first-tier suppliers, other upstream suppliers, workers, governments, third parties such as NGOs, recruitment agencies, auditing companies, social activists and consumers” (p. 8). ST helps examine the different types of MNCs’ stakeholders, their salience and their roles in tackling MS. Some corporations are part of multistakeholder ethical associations, such as the Ethical Trading Initiative (Ishaya et al., 2024). ST can help explore the effectiveness of these multistakeholder alliances and initiatives in tackling MS. ST can be used in three RDs for MS as presented in Table 5 (RD5-7) and Figure 3.

Extant SSSCM literature has used ST to show that corporations must address stakeholders’ demands for social sustainability in their SCs to gain legitimacy in the society wherein they operate (Mani et al., 2018b). This suggests that if MNCs fail to meet their stakeholders’ expectations regarding tackling MS, they may lose their legitimacy. As stakeholders’ awareness of MS increases, they will pressurize MNCs to disclose more information regarding their efforts to combat MS. This is supported by legislated MS reporting requirements from various legislations, such as the UK Modern Slavery Act (2015) and the Australia Modern Slavery Act (2018). Prior SSSCM studies demonstrated that suppliers in emerging or developing economies may respond to stakeholders’ demands for social sustainability through compliance or avoidance (Uttam et al., 2024). Thus, although there is increasing stakeholder pressure on MNCs to address MS in their SCs, this does not guarantee that their suppliers will adopt MS-free practices. Hence, it is imperative to understand suppliers’ perspectives on implementing MS-free practices, the challenges they may face and the assistance or incentives MNCs may offer to ensure adoption and implementation of these practices.

In addition, coercion from stakeholders can propel corporations to increase their sustainability awareness and adopt and implement socially sustainable practices in their SCs (Meixell and Luoma, 2015). NGOs and the media are the most influential stakeholders in corporations’ SC sustainability, followed by intermediate managers and employees within a firm (Meixell and Luoma, 2015). The diverse types and roles of stakeholders and their salience in the adoption of MS-free practices by MNCs must be understood. Future studies can investigate how different types of stakeholders may influence MNCs differently when adopting MS-free practices in SCs. Furthermore, SSSCM studies show that focal firms require “social management capabilities” to respond effectively to stakeholder pressures for sustainability in SCs, resolve legislative gaps appropriately and enhance their social performance (Huq et al., 2016, p. 1). There is a need to empirically investigate how MNCs can develop these capabilities and use stakeholder pressure as an opportunity to evaluate their SCs to identify any MS risks, make necessary changes in their operations and SCs, and check their compliance with MS legislations.

Prior SSSCM studies showed that stakeholders hold MNCs accountable for sustainability in SCs; if social concerns such as forced or child labor are found, stakeholders such as customers, NGOs, shareholders, labor unions, investors and the media can punish MNCs by boycotting, withdrawing their support or selling stock, resulting in financial losses and brand and reputational damage (Hofmann et al., 2014). Future empirical studies must explore how stakeholders might penalize MNCs with MS in their SCs and the financial and reputational damage they may suffer. Stakeholder salience and pressure influence corporate sustainability and sustainability reporting (Rudyanto and Siregar, 2018; Weber and Marley, 2012). Stakeholders’ power, legitimacy and urgency vary across GSC locations, and MNCs tend to focus on the highly salient stakeholders in their home countries (Kovacs, 2022). Stakeholders have pressed MNCs, such as Apple and Nike, to address child labor and worker exploitation in their SCs (Gualandris et al., 2015). Sokat and Altay (2022) showed that customer and investor stakeholders can boycott firms with MS in their SCs and impact their economic performance and corporate reputation. The collective insights from these previous studies can help future studies empirically examine how pressure from different types of stakeholders with different salience attributes can catalyze the adoption of MS-free practices in SCs (RD5). This can help MNCs to better understand and prioritize the expectations of their most salient stakeholders regarding MS, and identify stakeholders who can assist in identifying and addressing MS risks in their SCs.

Engaging with external stakeholders and developing collaborative capabilities between firms and stakeholders can help firms address sustainability concerns in their operations (Roscoe et al., 2020). In the context of MS, empirical evidence is required on how stakeholder engagement can help MNCs identify and resolve early warnings of MS risks. Future studies must investigate how stakeholder engagement and collaboration can increase awareness, knowledge creation, organizational learning (OL) and capability development, thereby helping MNCs to tackle MS. Stakeholders can assume different roles depending on their capabilities and help MNCs improve the sustainability of their SCs, including evaluating and verifying suppliers (Gualandris et al., 2015). Globally dispersed SCs make it challenging for MNCs to implement anti-MS policies and practices. It is important to understand how MNCs may engage and collaborate with external stakeholder experts to evaluate and verify their suppliers’ sustainability and better manage MS risks in SCs in different industries and countries. Liu et al. (2022) showed that stakeholder engagement and collaboration with different types of stakeholders can help firms tackle MS. MS is a multistakeholder problem requiring a multistakeholder approach and effort to resolve (Robb and Michailova, 2022). Firms can collaborate with stakeholders such as NGOs, governments, trade unions and competitors to combat MS (Stevenson and Cole, 2018). Future empirical studies should investigate how firms can use stakeholder engagement and collaboration to address MS in GSCs in various industries (RD6). This can inform MNCs regarding proactive engagement of external stakeholders to gain knowledge about MS and how to best eradicate it from SCs.

Sarkis et al. (2011) suggested future studies using globally oriented ST to examine SCs’ sustainability. To best capitalize on ST when analyzing GSCs, the theory must be applied beyond traditional stakeholder categorization in SC management (Kovacs, 2022; Sarkis et al., 2011). Sarkis et al. (2011) argued that “internationally focused stakeholder theory may also be more relevant as the globalization of supply chains have caused the stakeholder sphere to continue expanding” (p. 10). Focal firms and their head offices are typically located far from their SCs, and specific stakeholder groups in the SCs’ immediate environment may have better awareness of local sustainability concerns than focal firms (Kovacs, 2022). The author argues that “looking at stakeholders in various locations, and in the global supply chain, could indeed contribute to the rise of global product, process, but also environmental and social standards” (Kovacs, 2022, p. 317). From a global ST perspective, there is a need to understand how firms’ local and global stakeholders as well as SC partners can collaborate in shaping and fostering MS-free practices in GSCs, and work toward eradicating MS worldwide. Globally-focused ST analysis in MS research is logical given the globalized production and markets, global value chains led by MNCs that enable MS to occur, global reach of MNCs and increasing demands for global accountability of MNCs (Caspersz et al., 2022).

The stakeholder attributes of power, legitimacy and urgency vary across locations in GSCs (Kovacs, 2022). Therefore, research on MS and stakeholder salience across GSCs is required. Studies can explore how MNCs’ salient stakeholders can effectively contribute toward the formulation, adoption and implementation of anti-slavery standards and practices in geographically dispersed SCs. Future studies can use a globally-focused ST to identify and analyze the stakeholders involved in MS concerns in SCs, their diverse needs and expectations and how the different stakeholders’ capabilities could help MNCs tackle MS. There is a need to use international ST and empirically analyze MNCs and their local and global stakeholders in GSCs; the relationships between the stakeholders, how they influence each other dependent on their salience, how they can exert pressure and prompt MS-free practices in GSCs and how they can help tackle MS (RD7). This can foster an increased global stakeholder perspective, providing a comprehensive empirical understanding of the concerns and interests of diverse stakeholders regarding MS in SCs.

The resource-based view (RBV) theorizes the firm as a package of resources, and suggests that differences in firms’ performance are due to the heterogeneous tangible resources and intangible competencies they possess (Barney, 1991). The RBV also considers a firm’s reputation and image as a crucial intangible strategic resource, representing a vital source of competitive advantage (Barney, 1991). Although a few studies argue that the RBV is a suitable theoretical perspective for MS research (Geng et al., 2022; Mehmood et al., 2023; Stevenson and Cole, 2018), the theory has not yet been widely used. A firm’s resources and capabilities influence its capacity to address MS in its SCs (Geng et al., 2022). Corporations with more or better resources and capabilities can input more efforts into tackling MS in their SCs and may have better corporate sustainability performance (Geng et al., 2022). The RBV is relevant to MS research because it can help investigate the resources and capabilities MNCs require to address MS. The RBV has been used in CSR (Yadlapalli et al., 2018), SSCM (Benstead et al., 2022) and SSSCM (Mani et al., 2018a; Moxham and Kauppi, 2014) literature. These studies provide insights for future research using the RBV and explicitly focusing on MS. Future studies can use the RBV in three RDs for MS, as presented in Table 5 (RD8–10) and Figure 3.

Interorganizational learning (IOL) in SCs involves sharing and disseminating information and co-creating knowledge to gain competitive advantages (Sarkis et al., 2011). According to Yadlapalli et al. (2018), “when suppliers and buyers work together, they develop valuable, rare and hard-to-copy resources that improve social, environmental and economic performance” (p. 144). Nevertheless, it remains poorly understood how IOL and knowledge sharing about MS between firms and their SC partners can create resources and capabilities that provide competitive advantages to firms. MS is a relatively unfamiliar problem for firms and requires them to engage in OL (Simpson et al., 2021). As MS legislation requires firms to produce MS statements, firms must engage in OL to familiarize themselves with the new MS reporting requirements (Schaper and Pollach, 2021). The OL associated with MS reporting can provide competitive advantages to firms (Schaper and Pollach, 2021). Therefore, firms must perceive MS reporting as a catalyst (Hampton, 2019) to implement changes toward MS-free SCs. Although OL is crucial for change toward MS-free SCs, there is a lack of understanding of how corporations can use it as a valuable strategic resource that provides competitive advantages. Future studies can examine how firms can use MS reporting as an opportunity for OL and make substantive changes to address MS and achieve competitive advantages (RD8). This can provide insights into buyer–supplier learning and knowledge-sharing opportunities through MS reporting, helping MNCs tackle MS more effectively and gain competitive advantages.

Studies show that buying firms can gain competitive advantages through buyer–supplier collaborations in addressing social concerns in SCs (Luzzini et al., 2015), which can foster reliable long-term relationships, mitigate opportunism and unethical or illegal supplier behavior, and create unique capabilities that provide sustained competitive advantages to firms (Mani et al., 2018a; Pagell et al., 2010). Liu et al. (2022) reported that low-tier suppliers often lack the resources and capabilities to implement MS-free practices; buying firms must collaborate with suppliers, invest in their operations and provide the necessary training. Nonetheless, there is a lack of clarity on how buyer–supplier collaborations can help firms tackle MS and gain competitive advantages. There is a literature gap regarding how MS can be tackled through relationship-based sustainable sourcing strategies. Studies also show that MNCs can gain competitive advantages through governance mechanisms that promote sustainability in SCs, such as supplier selection, monitoring and development (Yadlapalli et al., 2018). Regarding MS, how sustainability governance mechanisms can help firms achieve MS-free SCs and gain competitive advantages must be understood. The collective insights from these previous studies can provide future directions for MS research. Future studies can empirically examine how MNCs can gain competitive advantages from MS-free SCs through buyer–supplier collaborations and governance mechanisms, such as supplier selection, monitoring and development (RD9). This can provide insights for MNCs to gain competitive advantages from MS-free SCs through buyer–supplier collaborations and various governance mechanisms.

The natural RBV (NRBV) examines how firms can derive competitive advantages based on their interaction with the natural environment and the low-income people worldwide (Benstead et al., 2022). Scholars have linked MS to environmental destruction, climate change and exploitation of the poor (Brown et al., 2021; Gold et al., 2015), and emphasized the need to examine SSCM at the base of the pyramid (BoP) (Khalid et al., 2015). It is necessary to empirically demonstrate that SCs that are MS-free; avoid exploitation of poor and vulnerable people; and avoid environmental destruction are crucial sources of competitive advantage for MNCs. Researchers may use NRBV to investigate how firms can achieve competitiveness from MS-free, and ecologically and societally sustainable operations, focusing on the MS-environment–BoP nexus (RD10). Recently, concerns regarding the environment, the poor and global socioeconomic imbalances have increased (Benstead et al., 2022). There is increasing societal pressure on MNCs to address labor and human rights violations in SCs (Vandenbroucke, 2024). Hence, this proposed RD can provide insights for MNCs to address these societal pressures and concerns.

Resource dependence theory (RDT) posits that firms have limited resources and become dependent on others, leading to interorganizational power relationships centered on resource exchange (Hillman et al., 2009). RDT is pertinent to SC research because it facilitates the examination of buyer–supplier relationships and risks of dependence (Mani et al., 2018a). RDT has not yet been extensively used in MS research, except Liu et al. (2022), who briefly used it to argue that collaborative and effective interdependent relationships between buyers and suppliers can help tackle MS. Gorton et al. (2023) argue that corporate reputation (CR) is a crucial intangible resource that is not directly under a firm’s control. CR is a resource dependence because it is partly determined by stakeholders’ perceptions and actors external to the firm, creating environmental dependency (Gorton et al., 2023). Moreover, the actions of suppliers of a firm can negatively impact its reputation and brand (Gorton et al., 2023). Socially SSCs can enhance a firm’s reputation and performance (Moxham and Kauppi, 2014), while allegations or evidence of MS can damage its reputation and corporate brand (Sokat and Altay, 2022). The RDT is applicable to MS research because it can help examine MNCs’ environmental dependencies resulting from suppliers using slave labor in SCs, negatively impacting MNCs’ reputation and brands. RDT has been used in SSCM (Hollos et al., 2012; Schnittfeld and Busch, 2016; Touboulic et al., 2014) and SSSCM (Mani et al., 2018a). The RDT can be used in three RDs for MS, as presented in Table 5 (RD11–13) and Figure 3.

The existing literature used RDT to show that corporations can improve resource dependence and sustainability in SCs through effective collaboration with suppliers (Sarkis et al., 2011), control mechanisms for managing suppliers’ sustainability (Schnittfeld and Busch, 2016) and long-term investments in suppliers in emerging economies who typically face financial challenges in implementing socially sustainable practices (Mani et al., 2018a). Sustainable suppliers are valuable resources which buying firms depend on, and firms develop suppliers’ capabilities to obtain preferential, long-term access to sustainable resources (Hollos et al., 2012). Corporations’ sustainability can be constrained by their resource dependencies, and they must reduce their dependence on unsustainable suppliers (Connelly et al., 2013). Developing a supplier portfolio can reduce dependencies in SCs (Shook et al., 2009). Human and labor rights violations or poor treatment of workers by suppliers can damage MNC reputation (Gorton et al., 2023). MNCs face high environmental dependence because they are judged by society based on the social impacts of their businesses and their SC partners (Gorton et al., 2023). Insights from these studies suggest that future studies can investigate the link between resource dependency and MS-free SCs. From the RDT perspective, MNCs must depend on and collaborate with suppliers that provide the essential resources they need for survival and growth. There is a literature gap regarding the entanglement of MNCs in MS, considering their dependency on suppliers for MS-free practices. Future studies must investigate the relationship between resource dependence and the social sustainability performance of SCs (i.e. SCs free from MS), how MNCs’ resource dependence in SCs influences their ability to have MS-free SCs and how MNCs could reduce their dependence on suppliers with high risks of MS (RD11). This RD can help generate actionable knowledge for MNCs to stipulate MS-free practices that suppliers must adhere to, which in turn can help MNCs prevent legal and reputational risks associated with MS. Such future studies can also offer insights into how MNCs can develop effective interdependence and collaboration with suppliers, use control mechanisms to manage suppliers’ social sustainability and make long-term investments in suppliers, all of which can give MNCs access to MS-free resources.

Connelly et al. (2013) observed a “supply chain creep” (p. 234), whereby suppliers from countries with relatively low production costs, such as China, are progressing upward in SCs, not only supplying raw materials but also conceptualizing, designing and manufacturing products for focal firms, thereby increasing MNCs’ dependencies and altering power dynamics in SCs. Studies show that emerging economies, such as China, have high MS risks and human and labor rights violations (Simpson et al., 2021). While increasing dependency on suppliers in some countries or regions are economically justifiable decisions by MNCs, from an RDT perspective, the potential risks associated with MS in MNCs’ SCs must be considered. Excessive dependence on suppliers that are moving up the SC and are located in countries with high MS risks can present challenges in tackling MS. Power dynamics between firms and suppliers influence the management of sustainability concerns in SCs (Touboulic et al., 2014), suggesting that “supply chain creep” may reduce the power of MNCs over suppliers and MNCs’ ability to influence sustainable practices within the SC. SC creep can also obscure the responsibilities of MNCs to ensure that their products are MS-free. Studies must investigate SC creep, increasing dependencies and changing power dynamics in SCs and their impact on MS risks for firms (RD12). This can help MNCs and their SC managers identify SC creep and the potential risks of MS in their SCs.

New technologies such as blockchain can have an impact on resource dependence dynamics in SCs (Nandi et al., 2021). Blockchain can improve transparency and traceability in SCs, which in turn can enhance sustainability (Long et al., 2023). As new technologies such as blockchain facilitate more traceability, visibility, transparency and trust in SCs (Rogerson and Parry, 2020), they may enhance information accuracy and sharing between SC partners, impacting the power structures and dynamics. With respect to MS, improved visibility can help SC managers resolve some of the underlying causes of MS, such as information asymmetry. Blockchain can help reduce deceptive recruitment of migrant workers (Christ and Helliar, 2021). There is a need to examine how blockchain can facilitate end-to-end SC digitization, MS-free resource acquisition and improve the implementation and monitoring of MS-free practices in SCs. There is a literature gap regarding how blockchain may impact resource dependence dynamics in SC and help improve MNCs’ relative dependence and power to ensure their SCs are MS-free. Future empirical studies must examine how new technologies such as blockchain may impact resource-dependence dynamics in the SC, facilitate MS-free resource acquisition by MNCs and improve implementation and monitoring of MS-free practices in SCs (RD13). Understanding the benefits of SC digitization can help practitioners make better decisions regarding investing in new technologies to improve SC visibility and eradicate MS.

Principal agent theory (PAT) explains the relationship between two parties, where one party (principal) commissions another party (agent) to undertake work, typically through a contract (Eisenhardt, 1989). Agency problems such as information asymmetry and goal conflict may occur, leading to opportunistic behavior and necessitating governance mechanisms to monitor the agent (Eisenhardt, 1989). Regarding SC relationships, PAT is centered on purchasing or sourcing activities, making it suitable for examining buyer–supplier relationships and SC phenomena (Fayezi et al., 2012). Except Liu et al. (2022), who briefly applied PAT to MS, the literature lacks the use of PAT to study MS. Although PAT can examine SC relationships and the impact of agency problems on implementing social sustainability in SCs (Yadlapalli et al., 2018), it has limitations when extended to complex, multitier SC networks (Zsidisin, 2022), which may explain its limited use in MS research. There is a need to apply PAT beyond buyer–supplier dyads; with GSCs as the level of analysis, to examine multiple principal–agent relationships in SC triads and networks (Fayezi et al., 2012; Zsidisin, 2022). The increasing MS legislation means that PAT becomes gradually more relevant for MS research as MNCs strive to minimize agency and litigation costs in SCs through governance mechanisms such as increased supplier monitoring, improved contracts and enhanced audit quality. PAT is applicable to MS research because GSCs span different contexts, including geographical, institutional and cultural, exacerbating agency problems between firms and suppliers, which can increase MS risks. PAT has been used in SSCM (Wilhelm et al., 2016) and CSR (Yadlapalli et al., 2018; Yu, 2008). Scholars can use PAT in three RDs for MS, as presented in Table 5 (RD14–16) and Figure 3.

Extant SSSCM research suggests that implementing socially sustainable practices in complex GSC networks can be challenging due to agency problems, such as goal conflicts and information asymmetries, causing opportunistic supplier behaviors (Yadlapalli et al., 2018). The principal and agent may have divergent attitudes toward risk, and suppliers may behave opportunistically and engage in socially unsustainable practices in their operations (Yadlapalli et al., 2018). Suppliers may engage in mock compliance with labor regulations to pass audits (Huq et al., 2016), or transmit inaccurate information regarding the implementation of socially responsible standards stipulated by the focal firm (Mani et al., 2018a). Due to information asymmetries, it is challenging for focal firms to verify suppliers’ actions, and firms lack timely and accurate information on whether suppliers’ operations are socially sustainable (Yadlapalli et al., 2018). Focusing specifically on MS, future empirical studies must explore buyer–supplier agency concerns in complex and multitier SCs and how they contribute to MS. Research on MS has shown that the complex, extended, fragmented, multitiered and opaque nature of GSCs makes them prone to MS risks (Gold et al., 2015). The cost and time pressures applied to suppliers also increase MS risks in SCs (Schaper and Pollach, 2021). Hence, future studies can examine buyer–supplier agency problems in GSCs, how they cause or enable MS to exist and how these agency problems can be solved to eliminate MS (RD14). This can help MNCs better understand agency problems in their SCs, how they contribute toward MS and how to address them.

Addressing agency concerns in multitiered SCs requires focal firms to delegate social responsibility to their first-tier suppliers who assume a dual agency role: in the primary agency role, they satisfy the buying firm’s sustainability obligations, and in the minor agency role, they disseminate sustainability practices to lower-tier suppliers and monitor them (Wilhelm et al., 2016). Firms must provide incentives to first-tier suppliers to fulfil both agency roles (Wilhelm et al., 2016). With respect to MS, this suggests that the double-agency role of first-tier suppliers can help MNCs tackle MS in globally dispersed and multitiered SCs. Studies demonstrate that institutional voids can lead to supplier decoupling from sustainability compliance (Kelling et al., 2021; Nath et al., 2020), suggesting that by assuming a double agency role, first-tier suppliers can help disseminate MS-free standards in the SC and monitor low-tier suppliers to ensure adoption of MS-free practices in their operations. This is critical because low-tier suppliers or subcontractors are typically small- to medium-sized operations situated in remote locations, with private operations shielded from institutional pressures (Wilhelm et al., 2016). Nevertheless, the double-agency role of first-tier suppliers raises concerns regarding whether they have sufficient bargaining power to influence lower-tier suppliers to adopt MS-free practices. Although Emberson et al. (2022) briefly mentioned the double-agency role of first-tier suppliers in combating MS, a more in-depth empirical analysis is required. Future research must explore the double agency role of first-tier suppliers in combating MS and helping MNCs overcome the agency and institutional challenges associated with disseminating MS-free practices in GSCs, and how MNCs can incentivize their first-tier suppliers (RD15). This can generate meaningful and actionable knowledge for MNCs to manage their multitiered SCs and delegate the implementation of MS-free practices to first-tier suppliers.

Studies show that numerous governance mechanisms can help address agency problems and improve social sustainability in SCs. These include (a) multiprincipal–supplier relationships with shared codes-of-conduct, incentives to dissuade opportunism and penalties or sanctions when necessary (Delbufalo and Bastl, 2018), and (b) supplier selection and development and buyer–supplier collaboration (Huq et al., 2014; Huq et al., 2016; Yadlapalli et al., 2018). In the context of MS, in-depth empirical research is required on how MNCs can collaborate and use shared codes of conduct with their shared suppliers to tackle MS. To implement socially responsible practices in SCs successfully, corporations must identify and select suitable and sustainable suppliers, develop and manage relationships with them and monitor their performance (Yadlapalli et al., 2018). There is an empirical literature gap regarding how MNCs can use supplier selection and development as governance mechanisms to mitigate agency problems in SCs and ensure that suppliers implement MS-free practices. It is noteworthy that the effectiveness of governance mechanisms suggested in the SSSCM literature may be limited because MS practices are illicit and usually covert or invisible and involve many labor intermediaries (Crane et al., 2022; Stevenson and Cole, 2018).

Few MS studies suggest various governance mechanisms to detect and combat slavery in suppliers’ operations, including supplier auditing, third-party certifications and codes of conduct (Flynn and Walker, 2021; Liu et al., 2022). By integrating diverse insights from previous studies, future research can scrutinize governance mechanisms to address agency problems that contribute to or facilitate the use of slave labor in SCs, and suggest the most effective governance mechanisms that MNCs can use to tackle MS (RD16). This can guide MNCs’ SC managers in their sourcing activities on the most effective governance mechanisms to address agency issues such as information asymmetry, goal conflicts and risk aversion and ensure the implementation of MS-free practices by suppliers.

TCE explains the cost and effort required for two parties to complete an economic transaction (Williamson, 1981). Transaction costs can be ex ante or ex post, and governance mechanisms can minimize these costs (Williamson, 2008). The TCE is based on two central assumptions of human behavior: opportunism and bounded rationality (Williamson, 1981). It considers transactions as the primary unit of analysis and uses contracts to minimize opportunistic behavior and transaction costs (Williamson, 1981). TCE has yet to be used in MS research and can be usefully applied. Due to the bounded rationality of buying firms and supplier opportunism, slave labor may be used in SCs. Therefore, TCE can help examine the different mechanisms that MNCs can use to manage their outsourcing relationships and mitigate opportunistic supplier behavior and the use of slave labor. TCE can examine critical elements of buyer–supplier relationships – transactions, transaction environments and suppliers – and the most suitable governance methods to minimize MS risks. TCE has been used in SSCM (Jiang, 2009a, 2009b; Meinlschmidt et al., 2018), SSSCM (Huq et al., 2014; Sancha et al., 2016) and CSR research (Yadlapalli et al., 2018). TCE can be used in four RDs for MS, as presented in Table 2 (RD17–20) and Figure 3.

SSSCM studies used TCE to show that bounded rationality of buying firms, environmental uncertainty and suppliers’ opportunistic behavior can cause problems in lower-tier SC sustainability management, resulting in high SCs transaction costs (Huq et al., 2014; Meinlschmidt et al., 2018; Sancha et al., 2016; Wang et al., 2015). Some buying firms have thousands of lower-tier suppliers in their SCs, making it costly and nearly unattainable for them to monitor these suppliers (Meinlschmidt et al., 2018). Implementing socially sustainable practices is associated with high uncertainty due to ex ante information asymmetry (e.g. the risk of selecting unsustainable or unsuitable suppliers owing to bounded rationality) and ex post costs (e.g. suppliers’ opportunistic behavior and monitoring suppliers) (Huq et al., 2014). Firms typically focus on the social sustainability of their immediate suppliers, neglecting lower-tier suppliers and subcontractors, which creates high transaction costs for firms (Huq et al., 2014). Future research must explore the ex ante and ex post costs of establishing and monitoring SC contracts to ensure MS-free SCs. TCE can be applied to investigate the potential costs, including reputation and brand damage, resulting from MS in SCs. Environmental uncertainty and lack of legal safeguarding increase the risk of supplier opportunism in SCs in emerging and developing economies (Wang et al., 2015). This implies that weak legal systems and unstable environments can increase supplier opportunism and the use of slave labor in SCs.

Suppliers may conceal violations and engage in mock compliance to pass audits; they hold two sets of timesheets, one that seems to comply with regulations and is shown to buying firms and auditors and one that reflects actual practice, which hinders SC sustainability (Huq et al., 2014). Mock compliance can lead to reputational damage for focal firms if leaked to the media (Huq et al., 2014). Suppliers may behave opportunistically to obtain cost advantages; their self-interest and deception can lead to the use of child labor and a failure to offer safe or healthy working environments (Sancha et al., 2016). Currently, there is a literature gap regarding the antecedents and consequences of supplier opportunism, the use of slave labor and the institutional contexts that enable opportunism. The extant SSCM literature suggests numerous governance structures to minimize supplier opportunism (Sancha et al., 2016; Yadlapalli et al., 2018). Building upon insights from these studies, opportunities exist for researchers to investigate how buying firms’ bounded rationality, environmental uncertainty and supplier opportunism can cause high transaction costs associated with MS, and explore the mechanisms firms may use to combat MS (RD17). Such research can offer valuable insights into how MNCs can implement MS-free practices in their SCs located in emerging or developing economies characterized by environmental uncertainties and supplier opportunism and minimize transaction risks and costs.

Studies show that audits may not effectively detect or rectify social concerns in SCs or sufficiently monitor suppliers’ sustainability performance, specifically for low-tier suppliers (Jiang, 2009a, 2009b; LeBaron et al., 2017; Meinlschmidt et al., 2018). Although MNCs use audits to monitor suppliers’ labor conditions and identify noncompliance, audits have become symbolic implementations that do not improve labor conditions (Vandenbroucke, 2024). For instance, Meinlschmidt et al. (2018) state that “although the Italian chocolate and confectionery producer Ferrero had banned child labor in its code of conduct and its suppliers had been independently audited, Ferrero was severely accused of exploitation and child labor at a sub-contractor in Romania” (p. 1889). Little is known about the effectiveness of audits in minimizing transaction costs due to buying firms’ bounded rationality and supplier opportunism which causes the use of slave labor. Moreover, previous studies have raised concerns regarding the capacity of buying firms to audit all their suppliers, considering the vast, multitiered and globally dispersed SCs (Meinlschmidt et al., 2018). Suppliers may subcontract work to subcontractors or unregulated factories without the buying firm’s cognizance (Stevenson and Cole, 2018).

Prior research also shows that supplier deception is common in auditing processes; to fulfill sustainability requirements from buying firms without incurring overhead cost increases, some supplier factories engage in audit fraud and double bookkeeping and train their workers to provide satisfactory or allowable answers in audit interviews, resulting in inaccurate audit results and lack of sustainability improvements (Jiang, 2009a, 2009b). Although MNCs may stipulate audits as part of their contracts with suppliers, the effectiveness of these audits in tackling MS requires further investigation. Thus, drawing on insights from prior literature, opportunities exist to investigate the effectiveness of audits in tackling MS in SCs. In addition, as MS legislation, reporting and auditing frequency increase in the future, this could lead to audit fatigue (LeBaron et al., 2017). There is a need to conduct in-depth empirical analysis of the effectiveness of audits in tackling MS in SCs across various industries and jurisdictions, and the risk of audit fraud and its antecedents and consequences in GSCs (RD18). This can help MNCs improve the effectiveness of their supplier audits and eliminate MS in their SCs.

Studies show that sustainable practices offer numerous benefits to firms, including mitigating reputational risks, strengthening brands and gaining new customers and markets (Sancha et al., 2016). However, TCE analyzes decision-making from an economic perspective and undervalues other triple bottom-line elements – social and environmental considerations (Connelly et al., 2011). Nevertheless, markets and economic transactions can be influenced by the “market for virtue” and socially responsible business practices; consumers may consider sustainable products superior (Connelly et al., 2011, p. 89). Firms implement sustainable practices when it makes economic sense to do so (Connelly et al., 2011). Although firms may economically perceive sustainability initiatives as costs and liabilities, they might view them to be worthwhile if they consider the markets’ social consciousness (Connelly et al., 2011). Currently, there is a lack of clarity regarding the economic justification for implementing MS-free practices in SCs. Banerjee (2021) argues that “the market for forced labor is vast both in terms of supply and demand, and it dwarfs any market for virtue that may exist for “slave-free” products” (p. 415). Similarly, LeBaron (2021) argues that MS is a structural phenomenon driven by wider business and societal issues that create demand for and supply of exploitable workers. The fundamental underlying dynamics that drive the demand for slave labor are concentrated MNC power, outsourcing, irresponsible sourcing practices and governance gaps, while the dynamics that drive supply are poverty, vulnerability and limited labor protection (LeBaron, 2021). This raises the question of whether the production, consumption, sale and purchase of “slave-free” products can overcome the significant underlying issues causing MS.

Furthermore, there is limited understanding of whether or how a market for virtue (i.e. slave-free products) could influence labor standards in SCs; how such a market could be created and function; and how MNCs can effectively signal their slavery-free products to the market. From a TCE perspective, managers must adopt a holistic approach to sourcing decisions, move beyond short-term transactions and costs and ensure that sourcing decisions provide economic value at the firm level long-term (Shook et al., 2009). Future studies can extend TCE by applying it to MS because such analysis goes beyond transaction costs to consider the benefits of MS-free SCs and products, and provide a more comprehensive analysis of the benefits that firms can gain. Future evidence-based studies could analyze the economic rationale for adopting MS-free practices in SCs and the commercial justification of MS-free initiatives in different industries (RD19). This knowledge can help corporations understand the commercial justification for MS-free initiatives in their SCs, which is important considering consumers’ increasing demand for products that are not tainted by slavery.

Prior research raises concerns regarding contracts’ effectiveness in ensuring suppliers’ social sustainability (Huq et al., 2014). Solely formal contracts may not ensure supplier adherence to social sustainability and human rights standards in GSCs; focal firms must also use informal relational mechanisms (Cao et al., 2024). The efficacy of supplier codes of conduct in enhancing labor conditions in GSCs is disputable, as their effectiveness is inconsistent and fails to improve labor conditions (Vandenbroucke, 2024). Studies also show that some buyer–supplier contract terms, such as low prices, shorter lead times and shorter contract duration, hinder suppliers’ ability to meet sustainable practice standards set by the buying firms, cause suppliers to enforce excessive overtime labor, disregard workers’ physical limits and underpay them (Jiang, 2009a, 2009b). Vandenbroucke (2024) states that “supplier opportunistic behavior may be caused by the purchasing practices of buyers, whose economic incentives drive them to choose cost-efficient suppliers and put important price pressure on their subcontractors. Unreasonably high and increasing production demands or high-powered productivity incentives also impact SC compliance, as incentives to cut corners to produce more and quicker are associated with inferior labor practices” (p. 320).

There is a lack of knowledge regarding how MNCs can structure their contracts with suppliers to dissuade or prevent use of slave labor. Future research must explore how SC contract terms may lead to labor exploitation in SCs and how contracts should be structured to minimize the risks of MS. MS studies show that price pressures cause suppliers to use cheap labor, and short lead times force them to hire short-term workers through unregulated labor intermediaries or subcontract to non-audited factories (Stevenson and Cole, 2018). However, little is known about contractual deterrence and MS-free GSCs, how MNCs can structure contracts to deter the use of slave labor by SC partners and the effectiveness of these contracts in diverse institutional settings. Legal enforceability and government support in different institutional contexts influence the effectiveness of contracts (Bai et al., 2016). Future studies can examine contractual deterrence and MS-free GSCs, how MNCs can structure contracts to deter the use of slave labor and the moderating effect of institutions (RD20). This research avenue can produce actionable knowledge necessary to improve contractual agreements between MNCs and their SC partners, make contracts effective in addressing MS and ensure that contract terms do not contribute toward MS risks. This is a worthwhile investigation because most SC activities are located in developing or emerging economies with institutional voids (Kelling et al., 2021), which increase MS risks and impact the effectiveness of SC contracts and MNCs’ ability to enforce the terms of contracts in courts.

This study used six well-established organizational theories to develop a multitheoretical framework and agenda for future research on MS. Literature reviews on MS reported that despite the increasing attention on this topic, there is a lack of theory-driven research (Han et al., 2022; Mehmood et al., 2023; Strand et al., 2023). Han et al. (2022) reported that “there has been relatively little theoretical research into modern slavery” (p. 15). Mehmood et al. (2023) argued that “there is a vast scope for future study on the subject of modern slavery, and such work should be driven by theory” (p. 18). Similarly, Strand et al. (2023) stated that “modern slavery research is on an upward trajectory” (p. 1), but, “there is a lack of theoretical underpinning across the articles” (p. 11). Although these literature reviews report a lack of theoretical foundations in MS research, there is a paucity of guidance on theories to be used in future MS studies. Mehmood et al. (2023) called for theoretical framework studies to provide directions for future MS research. MS scholars have advocated for borrowing theories from other domains to study MS (e.g. Gold et al., 2015). In this study, theories originating from sociology, strategic management, business ethics and economics were applied to MS to identify research opportunities. Investigating MS from different theoretical perspectives can deepen our knowledge of this phenomenon and advance the research field.

Researchers can investigate the proposed RDs using various methods and units of analysis. The literature review studies presented in subsection 4.1 (Table 3) identified the dominant methodologies and units of analyses used to study social issues in SCs (Govindan et al., 2021; Nakamba et al., 2017; Quarshie et al., 2016). Based on these reviews, the typically used methodologies are interviews, surveys, case studies and archival data. The dominant levels of analysis are government, organization, SC, group (e.g. organizational departments, customers, shareholders, activist groups and the general public) and individual levels (e.g. leaders, SC managers, purchasing executives and employees). These methodologies and analysis units can be extended to MS research. This is consistent with Strand et al. (2023), who argue that MS scholars should align their research with established theories and methodologies within the broader SC research field. Strand et al. (2023) lament the overreliance on secondary data in MS research but acknowledge the challenges associated with collecting primary data. Strand et al. (2023) state that “more studies collecting primary data with the direct voices of people with lived experiences of modern slavery, unions and workers are needed in the field. We strongly suggest getting away from secondary data analysis by introducing first-hand accounts and experiences” (p. 11). Primary data must also be collected from low-tier suppliers involved in production to gather their perspectives regarding MS, which is currently lacking in the extant MS research (Strand et al., 2023). Future studies must consider diverse products, industries, corporations, countries and regions.

Some theories may be more important than others for investigating MS. A recent review of MS literature found that IT is the typically used theory in the field (Strand et al., 2023) because it facilitates examining the influence of institutional contexts, institutional pressures on corporations and their responses (Christ et al., 2019; Diab, 2022; Flynn, 2020; Flynn and Walker, 2021; Gold et al., 2015). ST has been used in several MS studies (Liu et al., 2022; Robb and Michailova, 2022; Sokat and Altay, 2022). MS is a significant business and societal problem that must be collectively addressed by all stakeholders (Robb and Michailova, 2022). The introduction of MS laws in various jurisdictions over the past few years has generated external institutional and stakeholder pressures on MNCs to address MS in their SCs. Consequently, IT and ST have provided significant and relevant insights for studying MS.

The remaining theories used in this study – RBV, RDT, PAT and TCE – lack extensive use in MS research. This may be because these theories are primarily focused on the organization level, and corporations have only started addressing MS, which is becoming increasingly crucial in mainstream business (Flynn and Walker, 2021) and an urgent managerial concern (Rogerson et al., 2024). This indicates that organizational-level theories, such as the RBV, RDT, PAT and TCE, are becoming relevant and useful for studying MS and how corporations can tackle it.

Although the six theories have been individually applied to MS, future studies could combine multiple theories to perform more detailed and nuanced analyses. Halldórsson et al. (2015) argue that SC-related problems are typically complex. They cannot be adequately analyzed and explained by one theory, and studies must use several theories or one main theory complemented by one or more secondary theories. Furthermore, theories such as the RBV, PAT and TCE complement each other and facilitate a detailed analysis from multiple perspectives, advancing the understanding of SC-related phenomena (Halldórsson et al., 2015; Treiblmaier, 2018). Sarkis et al. (2011) argue that SC sustainability concerns must be examined within the context of the relationship between internal capabilities (as highlighted by the RBV) and external pressures (as emphasized by IT). Thus, future MS studies may combine the RBV and IT to examine how focal firms can invest in their internal capabilities to respond to institutional pressures more effectively. Mani et al. (2018a) and Sancha et al. (2016) used TCE and the RBV, which future MS studies can use to examine how focal firms may balance the short-term costs of supplier investment and development and the long-term benefits of such initiatives and competitive advantages that could be gained. Wilhelm et al. (2016) combine IT and PAT to examine how dissimilarities in institutional environments affect agency issues in SCs, which future MS studies can follow to investigate how different institutional contexts can create different agency problems hindering MS-free practices in multitiered SCs. Stakeholders can be external or internal to the MNC; thus, although this study applies ST at the environmental level, future studies can include firm-level analysis.

The literature review studies presented earlier in subsection 4.1 also identified infrequently used theories in studying SCs social issues – contingency theory, social network theory, population ecology theory, paradox theory, leadership theory, signaling theory and relational view theory. Future MS studies could also apply them or use them as secondary theories to conduct more detailed and nuanced analyses of MS.

This study makes several contributions to the MS literature. It develops a multitheoretical framework and research agenda comprising 20 theory-driven RDs for MS. This theoretical framework and the proposed RDs contribute to shaping future theory-driven MS research, bridge MS literature gaps and advance research on MS, a crucial problem impacting businesses and society. The theories presented in this study can help conduct empirical and theoretically rigorous research on MS in the SCs of various products, industries and firms. This study provides 12 secondary RDs presented in  Appendix, along with the 20 theory-driven RDs.

The study facilitates the development of MS research from the nascent to mature stages, helps to ensure congruence between existing MS literature and theory application and advances the research field (Edmondson and McManus, 2007). This study addresses the need for theory-based MS research (Caruana et al., 2021; Han et al., 2022; Strand et al., 2023).

This study’s results have several important implications. The proposed framework can be used as a practical tool to understand and manage MS risks. By considering MS through six theoretical perspectives, each with different assumptions, this study offers a comprehensive analysis of MS and provides diverse practical insights for practitioners, such as corporate leaders, SC managers and purchasing executives. The framework shows diverse, managerially pertinent concerns. It can help practitioners evaluate their SCs and develop strategies for tackling MS. It also brings MS – a critical social concern affecting SCs – to the forefront of firms’ strategic concerns. Examining social issues in SCs using the same theories as those applied to other organizational phenomena can make them central and crucial to organizational agendas and strategies (Moxham and Kauppi, 2014). Considering the globalization of production, MS is a major risk for focal firms (Caspersz et al., 2022). By using multiple theoretical lens to analyze MS, this study helps practitioners understand and manage MS risk in GSCs and create more comprehensive and integrated strategies for combating this problem. The six theoretical perspectives can equip practitioners with conceptual frameworks to guide their decisions, actions and strategies regarding MS risks, evaluate their SCs and formulate initiatives to tackle MS.

Future research inspired by this study could generate insights to enable regulators to formulate more rigorous laws for combating MS and explore ways to ensure these are adopted and enforced in countries with high MS risks. The proposed RDs can provide actionable knowledge for policymakers. For example, one RD suggests investigating and measuring institutional pressures for MS-free SCs across different products and industries and the responses of firms and their implications for MS. Such future studies may reveal the effectiveness or weaknesses of MS laws. Policymakers may benefit from such studies in improving MS laws and their enforcement. Another RD proposed researching how institutional voids affect the adoption, implementation and monitoring of MS-free practices in GSCs in different institutional contexts. This can inform policymakers on how to formulate effective laws for combating MS in contexts with institutional voids.

This study has some limitations. First, it used only six theories. Future studies could develop further research agendas for MS based on different sets of theories. Second, each theory is limited to a single-level analytical perspective. Future studies should apply theories to multiple levels of analysis. MS presents a multilevel governance challenge, it can have multilevel impacts at the global, national, organizational and SC levels (Burmester et al., 2019). Third, this study uses well-established theories to develop a research agenda. Extant theories may be limited in their capability to analyze MS because it differs from other social issues in SCs (Caruana et al., 2021). Future studies using the suggested theories can identify limitations and facilitate the development of new MS theories. Finally, this study did not combine and contrast the theories applied to MS. Future MS studies could use several complementary or contrasting theories.

MS is a contemporary and pressing global concern affecting focal firms, and is gaining increasing attention from governments, NGOs, the media, consumers and the general public. Hence, this study developed a theoretical framework and research agenda to provide a broad and robust theoretical foundation for future MS studies. Increased empirical research on MS in SCs is required in numerous contexts, such as in different products, industries, corporations, countries and regions. Strand et al. (2023) show that industry-focused studies have investigated MS in low-skilled and labor-intensive industries such as agriculture, fishing, forestry and textiles. Strand et al. (2023) argue that research is required in industries producing goods with a high risk of MS and those using recruitment agencies. As presented in subsection 2.2, International Labour Organization (ILO) et al. (2022) identified the sectors most affected by MS as services, manufacturing (i.e. extraction or transformation of raw materials in agriculture, fishing, forestry, mining and quarrying), construction and agriculture (i.e. farming agricultural commodities for agri-food SCs, and fruit and vegetable harvesting). Future MS studies must consider these industries. To date, most MS studies have been centered on the UK, USA and Australia, linked to country-specific MS legislation, neglecting to investigate MS offences in lower SCs directly (Strand et al., 2023). As presented in subsection 2.2, MS is prevalent in Asia-Pacific, Europe, Central Asia, Africa and the Americas [International Labour Organization (ILO) et al., 2022]. Future studies must investigate MS in SCs by using country-specific case studies from these regions. These studies may use various methods and units of analysis.

The six theories presented in this study provide a solid and broad foundation for future research on MS in SCs and offer practical insights for SC managers. Future studies can use these six theories individually or in combination to conduct more in-depth and nuanced studies. By applying insights from institutional, stakeholder, resource-based, resource dependence, agency and TCEs theories, this study provides 20 RDs on MS in SCs. The study also presents 12 secondary RDs for MS in  Appendix Table A1. This study invites future research on MS using the suggested theories and RDs, to advance knowledge about this problem and contribute toward addressing it.

The author would like to express gratitude to Z. Shailer for reading an earlier draft of this manuscript.

Declaration of interest statement: The Author declares that there is no conflict of interest.

Table A1