The European Commission, the EU's executive arm, said it was not satisfied with Warsaw's response to the action it launched in April over the regime.

After Poland's Law and Justice party took office in late 2015, it introduced sweeping reforms it insists are needed to tackle corruption and overhaul a judicial system still haunted by the communist era.

But Brussels has accused the government of threatening to undermine the principles it signed onto when Warsaw joined the EU.

It said at the time that judges would be punished simply for doing their jobs independently and this would have a "chilling effect" on legal freedoms.

The Commission gave Warsaw two months to respond to the initial action. "The Commission concluded that the response does not alleviate the legal concerns," it said Wednesday.

"The Polish authorities now have two months to take the necessary measures to comply with this reasoned opinion," the commission statement said.

"If Poland does not take appropriate measures, the Commission may decide to refer the case to the Court of Justice of the EU (ECJ)."

The case could result in fines.

Poland's government spokesman Piotr Muller questioned whether the action was appropriate for a European Commission due to end its mandate in October.

It "wasn't a good situation," Muller said.

Muller said the new disciplinary chamber at issue was created to guard against political interference when handling allegations against judges.

The EU has already launched unprecedented proceedings against Poland over "systemic threats" to the rule of law that could see its EU voting rights suspended.

Warsaw is already facing two similar procedures, one launched in July 2017 over reforms to lower courts and one from July 2018 relating to Supreme Court changes. Both of them have been referred to the ECJ.

These procedures are parallel to but separate from the more serious rule of law proceedings which the commission began in December 2017.