The EU country has been mired in crisis over a government bid to change how the Constitutional Court reaches its decisions, in a move that has sparked outrage at home and abroad.
A new law raised the bar needed for court rulings from a simple majority to a two-thirds majority of justices, while also requiring 13 judges to be present for the most contentious cases instead of nine as before.
But the court itself on Wednesday struck down the ruling as unconstitutional, pitting it against the government led by the Law and Justice (PiS) Party, which dismissed its judgement.
Nearly 54,000 users shared the constitutional court verdict on a dedicated Facebook site in the 24 hours after it was handed down.
The campaign urged Prime Minister Beata Szydlo to publish the verdict in Poland's Journal of Laws, a move that would render it binding.
With public anger growing, an impromptu street protest attracted around a thousand people, including opposition party members, Thursday evening outside the cabinet office in Warsaw.
Protesters used a projector to light up the building's facade with a copy of the Polish constitution. A day earlier they did the same with a copy of the verdict.
"A government that ignores court rulings, is quite simply undemocratic. It's putting itself above the constitution," Warsaw resident Magdalena Mikula-Mayer, 39, told AFP.
Szydlo had dismissed the verdict even before it was delivered, saying: "The statement that will be delivered by some of the judges of the Constitutional Court will not be a verdict in the legal sense of the term."
'Iranian ayatollah'
Foreign Minister Witold Waszczykowski on Thursday likened the top court's Chief Justice Andrzej Rzeplinski, a respected jurist who handed down the ruling, to an "Iranian ayatollah".
The government's refusal to abide by the judgement has set Poland on a collision course with the European Union, which launched an investigation into the reforms in January.
Warsaw could now face punitive measures over the situation.
Poland also said Thursday it would dispute a draft report by the Venice Commission a body of legal experts within the Council of Europe warning that the court reforms put democracy, human rights and the rule of law at risk.
The commission is due to publish its official report by Saturday.
Although the Council of Europe's findings are not binding, the European Union is likely to review them as part of its own unprecedented probe into the rule of law in Poland.
Opposition parties have claimed that the government's determination to force through the changes risks undermining democracy in the ex-communist nation of 38 million people.
"If the government doesn't abide by the constitutional court's ruling soon, we're dealing with the biggest crisis in the history of the republic and a constitutional coup d'etat," said Ryszard Petru, leader of the liberal Modern opposition party.
PiS has "fundamentally violated the constitution. Its contempt for the separation of powers... allows me to say without hesitation that democracy has stopped functioning in Poland," Radoslaw Markowski, a political scientist linked to Poland's Academy of Sciences, told AFP.
"There is no rule of law. Checks and balances on power are gone," he added.
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