Poland's icon of democracy, Lech Walesa, has lent his backing to protesters, who oppose a judicial reform pushed through by the country's right-wing government.
Organisers say the street demonstrations are gathering momentum in the conflict between Warsaw's ruling Law and Justice party and the judiciary.
Leading the battle is Polish judge Malgorzata Gersdorf who arrived for work on Tuesday rejecting a controversial law forcing her and dozens of other senior judges to retire early.
Surrounded by supporters she said her presence was not about politics but she was there to protect the rule of law. Chief Justice Gersdorf maintains her term of office is enshrined in the constitution.
Up to 40% of Supreme Court judges will be forced out, as part of changes that the government argues will help fight corruption and replace judges who date back to a communist era.
But the European Union has accused Poland's government of undermining judicial independence.
Prime Minister Mateusz Morawiecki has responded by saying it Poland has the right to develop its judicial system according to its own traditions.
Warsaw has one month to respond to an official EU challenge in the meantime a government official said it "could live with any further protests".