Hmmm, European Commission's action against Poland was most likely illegal

The Member States of the EU – individually or in conjunction – do not possess a formal right to evaluate how the judicial system is organized in another Member State. Such judgement would encroach upon a concept of fundamental importance to international relations, namely sovereignty. Thus Member States of the EU, when entering into an international agreement were not legally in a position to confer upon the European Commission the rights which they themselves did not possess in the first place.
Therefore, the European Commission has ascribed to itself powers, which it never received, nor could have received, even via an act of primary EU legislation.

Full article at Polish Diplomatic Review