This article shows how the ethical framing of the contemporary issue of modern slavery has evolved in UK construction, a sector in which there is a high risk of labor exploitation. It also examines how these framing dynamics have inhibited the emergence of a common framework of action to deal with the issue. We draw on both framing theory and the literature on the discursive construction of moral legitimacy. Our longitudinal analysis reveals that actors seeking to shape the debate bring (...) their own moral schemes to justify and construct the legitimacy of their frames. Actors cluster their views around five evolving frames: human rights issue (later shifting to hidden crime), moral issue, management issue (later shifting to human moral obligation), social justice issue, and decent work issue—which promote particular normative evaluations of what the issue is, who is responsible, and recommendations for action. Our study contributes to a dynamic and political understanding of the meaning making of modern slavery. We identify the antecedents and conditions that have forestalled the emergence of new patterns of action to tackle modern slavery in the UK construction sector thereby evidencing the effects of the interplay of morally competing frames on field-level change. (shrink)