Poland's presidency announced Tuesday that the top Supreme Court justice would retire on July 4 in line with a reform by the rightwing government that has been criticised by the EU.
Chief Justice Malgorzata Gersdorf, who has vowed not to leave her post, did not comment on the decision after meeting President Andrzej Duda, but her spokesman said she intended to return to court on Wednesday.
She had, however, named a temporary replacement to stand for her during her absence, spokesman Justice Michal Laskowski told reporters in Warsaw, naming him as Jozef Iwulski.
"The plans of the chief justice have not changed; she intends to be at work tomorrow and what will be her fate and her next decisions... I do not know," he added.
Gersdorf is one of a handful of top judges who have defied a series of controversial government reforms forcing them into retirement in a move which has drawn sharp criticism from the European Union.
Demonstrators rallying in support of the defiant judges were expected to take to the streets around the Supreme Court in Warsaw later on Tuesday as well as on Wednesday.
But a presidential aide told reporters Gersdorf was not expected to come to work on Wednesday, saying the Supreme Court was now "headed by Judge Jozef Iwulski".
The EU on Monday launched legal action against Poland over the Supreme Court reforms that critics have decried as unconstitutional.
The European Commission, the bloc's powerful executive arm, said the move to reduce the retirement age for Supreme Court judges from 70 to 65 would undermine judicial independence, breaching Poland's obligations under EU law.
Introduced by Poland's Law and Justice (PiS) government, the new retirement age came into force on Tuesday, compelling more than a third of the Supreme Court's 73 judges to step down.
Poland has a month to respond to the commission's legal challenge, in what is the first stage of a procedure that could end up in the European Court of Justice (EJC), the bloc's top tribunal.
But the PiS government has refused to back down, insisting the changes are needed to tackle corruption and overhaul a judicial system still haunted by the communist era
Chief Justice Malgorzata Gersdorf is one of a handful of top judges who have defied changes by Poland's right-wing government forcing them into early retirement