© Radek Pietruszka/EPAThe Polish prime minister Mateusz Morawiecki, arriving at an EU-western Balkans summit in Slovenia on Wednesday.
The tribunal, whose legitimacy is contested following multiple appointments of judges loyal to the ruling nationalist Law and Justice (PiS) party, said on Thursday some provisions of EU treaties and EU court rulings clashed with Poland's highest law.
"This is a legal revolution," said René Repasi, professor of international and European law at Erasmus university in Rotterdam. "Admittedly it's a captured court, but this is furthest step towards a legal exit from the EU ever taken by a national court."
The PiS-led government is embroiled in a lengthening and increasingly acrimonious series of disputes with the 27-member bloc on questions ranging from judicial reforms and media freedom to LGBT rights.
The Polish prime minister, Mateusz Morawiecki, brought the case in March, arguing Brussels has no right to interfere with the judicial systems of EU member states and the government's reforms were needed to remove communist-era influences.
Warsaw denies having any influence over court decisions but the government has been widely accused of politicising the courts, including the tribunal, which began hearing the case in August but had twice deferred its decision.
The primacy of European laws over national ones is a key tenet of European integration and Polish opposition politicians have repeatedly said challenging it jeopardises Poland's long-term future in the EU and also the stability of the bloc itself.
"The primacy of constitutional law over other sources of law results directly from the constitution of the Republic of Poland," government spokesman Piotr Müller tweeted. "Today (once again) this has been clearly confirmed by the constitutional tribunal."
Daniel Freund, a German MEP who sits on the European parliament's budgetary committee, said Poland was "saying goodbye to the European legal order" and demanded financial consequences as soon as the judgment became legally binding.
"Without European legal order, there can be no payment of EU subsidies," he said, adding the approval of Poland's recovery plan by the European Commission was now also "an absolute taboo. We cannot transfer billions to a member state without being able to legally ensure that the money reaches those for whom it is intended."
Comment: EU implicitly threatens Hungary and Poland to change rule of law if they want recovery money payout
Two judges on the tribunal dissented from the decision, but a majority said Poland's EU membership did not give EU courts supreme legal authority, and did not mean Poland had shifted its sovereignty to the EU.
No state authority in Poland could consent to external limitation of its powers, they said. Representatives of the country's human rights commissioner argued, however, that Poland had agreed to respect the EU legal order when it joined the bloc in 2004.
"It's a confederation of anti-democratic forces against Poland's membership in the European Union," Michał Wawrykiewicz, a pro-European lawyer critical of the government, tweeted, calling it a "black day" in the country's history.
Laurent Pech, professor of European law at Middlesex university, said Polish authorities had "engineered an (unconstitutional) Polexit from EU legal order" to "establish a Soviet-style justice system so autocratisation can happen undisturbed".
But a deputy foreign minister, Paweł Jabłoński, insisted that a ruling that recognised the primacy of the national constitution would not infringe EU membership treaties, arguing it would instead redefine them.
The European parliament last month adopted a resolution calling on Morawiecki to drop the case, stressing the "fundamental nature of primacy of EU law as a cornerstone principle of EU law".
The ruling of the tribunal, whose president, Julia Przylębska, is a government supporter, said the constitution was supreme law in Poland and every international agreement or treaty, being lower in rank, must respect that supreme law.
Government critics had earlier suggested the repeated delays to the tribunal's ruling were an attempt by Warsaw to put pressure on Brussels to approve Poland's plans for spending €57bn (£48bn) in EU recovery funds to help restart growth hit by the pandemic.
Comment: Poland's objections to EU supremacy reveal just how much power other member states gave away. And, if we look at 'developments' in those other countries, one can understand why Poland wants to stop their country going the same route: