Legal uncertainty may hinder the effective implementation of public policies. Still, the political and legal dynamics that underpin its persistence are underexplored. This article proposes that legal uncertainty is more likely to persist in multi-level political and legal systems where actors with authority on the same issue hold different interpretations of rules. Also, it suggests that, under these conditions, actors can use legal uncertainty as an opportunity to advance their own interests. We illustrate this argument by investigating the legal uncertainty concerning EU citizens' access to social benefits in Germany. Through the analysis of social legislation and courts' rulings, the article shows that different interpretations of EU law by domestic actors hindered the possibilities of settling uncertainty: national courts of different levels used litigation processes and referrals to the Court of Justice of the European Union to advance their legal interpretations and the German government profited from the uncertainty to exclude EU citizens from social benefits.