However, the European Court of Justice left it to Poland's highest court to determine whether the new Disciplinary Chamber is independent of influence from the nations' legislative and executive powers.
In Poland, both sides of the heated dispute around the ruling party's controversial changes to the country's judiciary declared victory upon hearing the verdict.
The head of the Supreme Court, Malgorzata Gersdorf, said the EU court clearly shared concerns over the new chamber, which is part of the Supreme Court. She vowed action aiming to "restore trust" in Poland's top court and its judicial bodies.
The right-wing government, however, said the ruling, which referred the matter back to Poland's judges, was a clear sign that the EU court believes it has no jurisdiction to assess the justice systems of member nations. Poland's ruling Law and Justice party has been voicing that opinion ever since it started to introduce changes to the judiciary when it took power in 2015.
The EU court's ruling also implied there are questions about the independence of another top body in Poland, the National Council of the Judiciary, which proposes judges for court positions, including on the Supreme Court, and is supposed to protect their independence.
Human rights group Amnesty International noted it has documented cases where judges and prosecutors have been "harassed or subjected to politically motivated disciplinary investigations and smear campaigns."
"This interference with the independence of judiciary must end immediately," Amnesty International said.
Tuesday's ruling came in response to questions by Poland's Supreme Court regarding the legality of its Disciplinary Chamber, which was introduced by the ruling party. The chamber can potentially punish judges for failures in their jobs and in their behavior.
Many of those appointed to the chamber were recommended by the ruling party, which has been condemned by EU leaders for meddling in the country's legal system and threatening judicial independence.
The European court is still to rule on judicial independence in Poland in a separate case brought by the European Commission, the EU's executive body.
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