The European Court of Justice says that a new disciplinary regime for judges could enable political influence over the judiciary.
Poland's new disciplinary regime for high court judges is in breach of European Union law, Europe's highest court has ruled,
The European Court of Justice found on Thursday that Poland had failed to fulfill its obligations and upheld complaints about the judicial reforms by the European Commission.
"The disciplinary system allows that the content of the judicial decisions adopted by the judges of the ordinary courts can be qualified as a disciplinary offense," it said.
"It could thus be used for the purposes of political control of judicial decisions or of pressure on judges in order to influence their decisions and undermine the independence of the courts concerned."
The ruling is the latest salvo in a long-running battle between Brussels and Poland since the right-wing Law & Justice (PiS) swept to power in elections in 2015.
Poland's government has accused the EU of being politically motivated against Warsaw, echoing the criticisms of other recalcitrant EU states such as Viktor Orban's Hungary.
PiS has brought in sweeping changes to the judiciary over the past six years, including an overhaul of the way judges are appointed to the country's supreme court.
Critics accuse the government of seeking to tie the hands of independent judges that would challenge controversial reforms and put PiS allies into key positions in the legal system.
Jakob Jaraczewski, a researcher coordinator at Democracy Reporting International, told Euronews that the judicial changes in Poland risk jeopardising law and order within the whole EU.
"This system causes, in fact, danger to the entire EU legal system. As the disciplinary proceedings against judges, in particular, the disciplinary proceedings against judges over the content of their decisions could lead to a chilling effect," Jaraczewski said.
"And that chilling effect may impact the way Polish judges interact with European Union law and whether they send cases to the court of the European Union. The current system imperils them from doing so, and that, in turn, endangers the entire EU legal order."
The researcher added that the Law and Justice party's actions give the impression that the country is gradually moving away from the EU, but even if that is the case, that isn't what the Polish people want.
"There is no broader will in Polish society to quit the European Union, and I believe that many people who support the Law and Justice party over its economic and social policies, at the same time are very keen to stay in the EU to enjoy freedom of movement, to enjoy the common market and so on," Jaraczewski told Euronews.
Poland is yet to respond to the ruling but is bound as an EU member to comply with judgments of the ECJ, and may face financial penalties if it does not.
Euronews has reached out to the Polish government for comment.