Since the Lisbon Treaty, research on parliaments in EU affairs turned to the regional level, but few studies ask how subnational legislators engage with the substance of EU policies. We examine this topic based on statements by the parliamentary groups in all German Landtage concerning the reform of the Posted Workers Directive, which became particularly salient when the European Court of Justice liberalized wage clauses in state procurement law. Under which conditions did the parliamentary groups support the reform? Our configurational analysis reveals that a left party identity is the only necessary attribute for support, and that it becomes sufficient in conjunction with the group being in opposition or with state policy being affected by European jurisprudence. We find little evidence that the local economic context mattered. The results partly confirm research on the Europeanization of state procurement law but highlight the importance of policy shaping from below.