A landmark ruling by Poland's top court challenging the primacy of EU law has entered into force.

The decision was published in the Official Gazette on Tuesday, making it legally binding.

The Constitutional Court ruled last week that parts of EU law were "incompatible" with the Polish constitution — giving national law primacy and undermining a key tenet of EU law.

The ruling has been heavily criticized by Brussels, which has hadd a strained relationship with Warsaw since the right-wing populist Law and Justice (PiS) party came to power in 2015.

"It has to clear: You are a member of a club, you have to abide by the rules of the club. And the most important rule of the club is that the European law is over national law," the EU's top diplomat, Josep Borrell, told Reuters. He added that the bloc would respond to the ruling with "a firm answer."

No 'Polexit,' says Poland

The case has also fueled speculation that Poland may one day stage a "Polexit" and leave the 27-nation bloc.

Deputy Foreign Minister Marcin Przydacz told DW that Poland had no such plans.

"We are a member of the EU, we going to stay in the EU," he said. "Ninety percent of Poles support our membership in the EU and also the government supports our membership."

He also accused the opposition, led by former European Commission head Donald Tusk, of spreading rumors about a Polexit.

Tens of thousands of Poles took part in rallies on Sunday in support of their country's EU membership. At the demonstration in Warsaw, Tusk accused PiS of putting Poland's future in Europe at risk.

Clashes over judicial reform

The ruling in the Constitutional Court had warned EU institutions not to "act beyond the scope of their competences" by interfering with Poland's changes to the judiciary.

Warsaw and Brussels have long locked horns over the policies, which the EU says undermine the independence of the courts. Poland, on the other hand, says they are necessary to curb corruption in the judicial system.

Media freedom, LGBTQ rights and migration have also proved sources of conflict.

nm/wd (Reuters, AFP, dpa)