Sub-supplier's sustainability management in multi-tier supply chains: A systematic literature review on the contingency variables, and a conceptual framework

Sub-suppliers may violate sustainability standards for a variety of motivations, and focal firms' neglecting of sub-suppliers’ sustainability violation despite stakeholder pressures to establish sustainability compliance at sub-supplier level can bring several tangible and intangible risks to focal firms. Focal firms apply sub-supplier's sustainability management (SSM) approaches to extend sustainability to sub-suppliers. As sustainable supply chain management is fundamentally context-dependent, a set of contingency variables are expected to impact the effectiveness of the SSM approaches. Through an up-to-date, comprehensive review of the literature on multi-tier, sustainable supply chain management (MT-SSCM), 37 contingency variables influencing the effectiveness of the SSM approaches in multi-tier supply chain are identified. These variables are then clustered in two stages based on their similarity in terms of their common themes/points for more efficient analysis. Propositions are formulated to explain the way variation in the contingency variables impacts the effectiveness of each SSM approach, when each SSM approach is an effective approach with regard to the contingency variables, the sub-supplier's motivations in not complying with sustainability requirements and the risks of ignoring sub-supplier's noncompliance with sustainability requirements for focal firm. A conceptual framework is built according to the results and findings of the study. Detailed practical implications are also presented to provide managerial insights for supply chain managers. Finally, possible future research directions, that are linked to identified research gaps, are discussed.