Poland's Constitutional Tribunal has breached core principles of European Union (EU) law, the European Court of Justice (ECJ) ruled on Thursday.

The court also found the tribunal cannot be considered independent or impartial because of serious irregularities in the appointment of judges.

The tribunal, dominated by judges appointed under the former nationalist Law and Justice (PiS) government, had previously declared Poland's constitution superior to EU law , ignoring ECJ decissions and case law.

European Council challenged Poland at ECJ

The case stems from two 2021 Polish tribunal rulings rejecting ECJ decisions as unconstitutional, claiming the ECJ overstepped by interfering in Poland's judiciary.

Brussels challenged those rulings, and the current pro-European government says it does not recognize them.

On Thursday, the ECJ ruled that Poland cannot disregard binding EU values, which all member states must uphold.

The court also criticized the way three of the judges and the tribunal's president were appointed under the former ruling party.

PiS drastically transformed the country's justice system, establishing political control over top courts such as the Constitutional Tribunal and the Supreme Court.

Polish tribunal remains defiant

The PiS lost power with the election of pro-European Prime Minister Donald Tusk in 2023, but his government has so far failed to roll back the changes, blocked by two subsequent nationalist presidents who support the PiS overhaul of courts.

On Thursday, Justice Minister Waldemar Zurek wrote on social media that the ECJ judgment obliged the state to take action, and the government was prepared to act.

The tribunal itself said the judgment had no impact on its functioning and that the European court had no authority over it.

Edited by: Dmytro Hubenko