This article focuses on the Supply Chain Law Initiative in Germany (SCLI)/Initiative Lieferkettengesetz as a case of global justice advocacy. The SCLI was a campaign by German civil society organizations that advocated for a law that would make it mandatory for corporations active in Germany to respect human, labor, and environmental rights along their supply chains. This research explores the strategies for advocacy used by the SCLI in the process of effective law-making. It also investigates the role of the SCLI in the context of global labor solidarity. The research results show that although this new law has some shortcomings in terms of international human rights standards, it has achieved partial progress as one of the most successful examples of alliance building between unions and civil society organizations in Germany. The SCLI has brought about a paradigm shift from voluntary towards mandatory due diligence. This experience can be carried one step further to accomplish a supply chain law at the European Union level. The authors argue that the SCLI experience opens up a new stage for rethinking the structural dilemma of unions in Germany in choosing between global solidarity and national corporatist social partnership.