The European Court of Justice has ordered Poland to reverse a law lowering the retirement age for Supreme Court judges, as an interim measure pending its judgement on the controversial reform.

The European Commission had referred Poland to the European Union's top court, arguing that the new law is in breach of fundamental EU values.

Brussels and Warsaw have been at loggerheads since late 2015 due to concerns that reforms introduced by Poland's conservative government place the judiciary under excessive political influence.

The reforms lower the retirement age of Supreme Court judges from 70 to 65, a measure that has triggered the departure of 21 judges.

Poland's ruling Law and Justice party (PiS) argues that it is purging the court of corrupt judges, but opponents accuse it of trying to remove critical voices. PiS is also of the opinion that, under EU rules, the organization of the judiciary is a national matter.