The European Union's top court has ordered Poland to reverse a purge the country's supreme court judges and halt their planned replacement with officials friendly to the government.

The European Court of Justice (ECJ) issued an injunction stopping the new law on Friday, freezing any changes to the judicial appointment system and ordering the reinstatement of sacked judges.

Since coming to power in 2015, Poland’s right-wing populist Law and Justice governing party has pushed through a series of controversial changes to judicial appointments that critics say put too much power in the hands of the government and endangers the independence of the judiciary.

The numerous changes give the governing majority in parliament greater power over judicial appointments, while another new law also forced around a third of the country’s supreme court judges into early retirement earlier this year.

The policies, which the Government says are simply long overdue reforms to an out-of-date judiciary, have attracted the ire of the European Commission, which says they breach the EU's charter of fundamental rights.

The Commission has started a legal process to censure Poland that would suspend the country's voting rights at the European Council if it is taken to its final conclusion.

Speaking on the sidelines of the European Council summit in Brussels, Poland's prime minister Mateusz Morawiecki told reporters:

It is alarming that, despite the rule of law being one of the cornerstones of the EU, things have gone this far Covadonga de la Campa, Amnesty

"In the last hours... a notification arrived from the European Court of Justice, I can say that certainly after thorough analysis we will take a position."

Poland could appeal the decision, and is reportedly likely to do so.

Human rights NGOs and politicians welcomed the intervention by the EU court. Covadonga de la Campa, interim director of Amnesty International’s European Institutions Office, said:

“Today’s court order makes it clear that it is unacceptable for Poland to ignore the EU’s most fundamental principles, in defiance of ongoing legal proceedings before the EU’s top court. Anything but immediate and full compliance with this binding court order would clearly show, once again, that the Polish authorities have complete disregard for the rule of law.”

“Polish authorities have been hastily appointing new judges despite the ongoing infringement case and Article 7 proceedings. It is alarming that, despite the rule of law being one of the cornerstones of the EU, things have gone this far.”

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She added: “Ousting a third of the Supreme Court judges is nothing but a purge and an attempt to assert political control over the judiciary. The European Commission’s move to halt the government’s actions is a welcome step on an issue, which is of great importance not only for Poland but also for the European Union as a whole.”

Guy Verhofstadt, the leader of the Liberal group in the European Parliament, said the Polish government had "crossed a red line by attempting to politicise Poland's Supreme Court".

"The European Court of Justice today took an important step in suspending the legislation in question until a final judgment can be made," he added.