The European Union takes Poland to the bloc's top court to stop alleged breaches of the independence of the country's supreme court.
The European Union sued Poland on Monday in the EU's highest court over its ruling party's changes to the judiciary, which the bloc believes violates the independence of the courts.
"The European Commission maintains that the Polish law on the Supreme Court is incompatible with EU law as it undermines the principle of judicial independence, including the irremovability of judges," the EU's executive Commission said in announcing the move.
The new Polish law lowers the retirement age of Supreme Court judges from 70 to 65 years, putting 27 out of 72 sitting judges at risk of being forced to retire.
The mandate of the head of the Supreme Court would be prematurely terminated.
Situation echoes that of Hungary
The Commission asked the Luxembourg-based European Court of Justice to suspend the application of the law until it reaches a verdict to prevent the forced retirement of the judges and the appointment of new ones in their place.
Poland was suspended last Monday from the European Network of Councils for the Judiciary, which decided the Polish council is no longer independent because it is now appointed by politicians, rather than judges as before.
Poland's situation echoes that of Hungary, which the European Parliament sanctioned earlier this month for flouting EU rules on democracy, civil rights and corruption.
Changes aimed to tackle corruption?
The new retirement age, introduced by Poland's Law and Justice (PiS) government, comes into force in July and would require more than a third of current Supreme Court judges to step down.
The PiS government insists the changes are needed to tackle corruption and overhaul a judicial system still haunted by the communist era.
The EU and the Warsaw government's Polish critics argue these measure undermine the division of powers and therefore threaten democracy and the rule of law.
In December, Brussels triggered unprecedented proceedings against Poland under Article 7 of the EU treaty over "systemic threats" to the rule of law, which could eventually see Warsaw's EU voting rights suspended.