The move comes after the European Commission voiced concern that new rules undermine the independence of Polish judges.
But Polish government spokesman Piotr Müller said on Tuesday that the changes introduced by Poland’s ruling conservatives are compliant with EU law.
Tuesday’s move by the European Commission comes after it on October 10 decided to refer Poland to the EU's top court over new disciplinary rules for judges, the latest step in a prolonged dispute over alleged rule-of-law breaches.
Last April the Commission said that new Polish legal regulations made it possible "to subject ordinary court judges to disciplinary investigations, procedures and ultimately sanctions, on account of the content of their judicial decisions."
The EU's executive also said at the time that the new Polish “disciplinary regime does not guarantee the independence and impartiality of the Disciplinary Chamber of the Supreme Court which reviews decisions taken in disciplinary proceedings against judges.”
Poland's governing Law and Justice party, which came to power in late 2015, has insisted that sweeping changes are needed to reform an inefficient and sometimes corrupt judicial system tainted by the communist past.
Poland’s prime minister argued in January that some of the legal changes made by his conservative government have met with criticism abroad because they are not understood in Western Europe.