Polish judge Malgorzata Gersdorf walked into the Supreme Court building on Wednesday morning, defying new legislation forcing her to retire as court president and putting the judiciary on a collision course with the government.
Supporters chanting "constitution" and singing the Polish national anthem surrounded her at the entrance as she told reporters: "My presence here is not about politics, I am here to protect the rule of law."
The is at the centre of mounting conflict between Warsaw's ruling Law and Justice party (PiS) and the European Union, which accuses Poland of trying to gain political control of the judiciary and of subverting basic democratic standards.
Under the new rules, which came into affect at midnight, up to a third of Supreme Court judges including 65-year-old Gersdorf could be forced to retire unless they are granted an extension by President Andrzej Duda, a PiS ally.
Gersdorf, who has been the president of the Supreme Court since 2014, believes the legislation is unconstitutional and cannot be implemented.
Opponents of the reforms planned demonstrations on Wednesday. Among them is Lech Walesa, the Nobel Peace Prize Laureate and former president who is credited with bringing down communism when he was Solidarity trade union chief.
Through legislation and personnel changes, PiS has already taken de facto control of much of the judicial system since coming into power in 2015, including the constitutional tribunal and prosecutors, who now report directly to the justice minister.
The party argues this is needed to address ineffectiveness in a system steeped in communist-era mentality and power structures.
Critics at home and abroad accuse PiS of seeking control over courts for political gain, and say its policies, which also include tighter control of public media, amount to a shift towards authoritarian rule.
The conflict has isolated Poland within the EU, where most governments are critical, while also exposing the bloc's inability to rein in governments it believes contradict core EU values.
The European Commission opened a fresh legal case against Poland over the Supreme Court changes on Monday, saying that they undermine judicial independence in the largest formerly communist member of the EU.
Warsaw faces the threat of losing its voting rights in the bloc under a procedure launched late last year over judiciary reforms. Hungary, also facing criticism over democratic standards, has pledged to block such a move.
The eurosceptic PiS government rejects criticism, saying EU treaties do not give Brussels institutions the power to influence national matters such as the judiciary.
"Let me mention a fundamental issue. The court system ... is an entirely internal matter," PiS leader Jaroslaw Kaczynski was quoted by the PAP news agency on Tuesday as telling Gazeta Polska newspaper.
The party's standing in polls has held steady at around 40 percent throughout the dispute, well above any single rival party.