PurposeThere is still significant variation in firms' efforts to address modern slavery issues in supply chains despite the importance of this grand challenge. This research adopts the awareness-motivation-capability (AMC) framework to investigate AMC-related factors that help to explain this variation.Design/methodology/approachThe authors hypothesize how AMC-related factors, including media coverage of modern slavery issues, slavery risks in supply chains and corporate sustainability performance, are related to firms' efforts to address modern slavery in supply chains. The proposed hypotheses are tested based on 201 UK firms' modern slavery statements and additional secondary data collected from Factiva, Factset Revere, The Global Slavery Index, Worldscope and Sustainalytics.FindingsConsistent with the AMC perspective, the test results show that firms put more effort into addressing supply chain modern slavery issues when there is greater media coverage of these issues, when firms source from countries with higher slavery risks, and when firms have better corporate sustainability performance. Additional analysis further suggests that firms' financial performance is not related to their efforts to address modern slavery issues.Originality/valueThis is the first study adopting the AMC framework to investigate firms' efforts to address modern slavery in supply chains. This investigation provides important implications for researchers studying firm behaviors related to modern slavery issues and for policymakers designing policies that enable firms to address these issues, in view of their awareness, motivation and capability.