In May 2020, the German Constitutional Court ruled that an ECB stimulus programme was partly contrary to Germany's national constitution.
This judgement risked jeopardizing the European Union's legal order, the European Court of Justice (ECJ) - the bloc's top court - had said at the time, DPA reported.
Based on the same reasoning, the commission sent a letter of formal notice to Berlin, arguing that "the judgment of the German Constitutional Court constitutes a serious precedent, both for the future practice of the German Constitutional court itself, and for the supreme and constitutional courts and tribunals of other member states," according to a press statement.
The ruling was the first time the German top court had gone against findings by the ECJ, which had previously declared the multibillion-euro bond-buying programme compliant with EU law.
Germany has two months to respond to the concerns. The commission could ultimately take Germany to the bloc's top court.