The European Commission has opened an unprecedented inquiry into whether new Polish laws break EU democracy rules.
Vice-President Frans Timmermans announced a “preliminary assessment” under the EU’s “rule of law mechanism“.
Critics of Poland’s right-wing government protested at changes to the constitutional court and media laws.
The EU mechanism allows the Commission to press a member state to change any measure considered a “systemic threat” to fundamental EU values.
The step comes after President Andrzej Duda approved controversial laws enabling the conservative Law and Justice (PiS) government to appoint the heads of public TV and radio, and choose judges for Poland’s constitutional court.
Addressing the Polish parliament on Wednesday, Prime Minister Beata Szydlo denied that her government had violated democratic norms.
She said it was carrying out a programme that Poles chose in a democratic election in October.
Under the EU’s rule of law mechanism adopted in 2014, a state’s voting rights in the EU Council – where government ministers shape EU policy – can be suspended.