While blockchain was designed as a ledger for cryptocurrency transactions, it can record transactions of anything of value. Blockchain is increasingly used to prove the integrity of commodities, tracing their supply chain journey from the source to the end user. Yet, transferring this technology from a cryptocurrency context to a supply chain setting is not without difficulties. This article explores the implications for multinational and transnational companies in using blockchain as a means to address modern slavery. The paper identifies five challenges: verification, inclusion, trust, privacy, and normativity.