France and Germany reiterated their support for the EU Commission but Hungary has welcomed the Polish ruling, calling on the bloc to respect national sovereignty.
The dispute over the ruling by Poland's constitutional court that the country's laws have primacy over those of the European Union rumbled on Saturday as Hungary, France and Germany came out in support of different sides.
The Polish verdict on Thursday drew swift condemnation from the EU executive and the main parties in the European Parliament. One commentator described it as a "nuclear strike on the EU legal order".
It also ratcheted up fears of a "Polexit".
The case had been launched by Prime Minister Mateusz Morawiecki as part of the ongoing dispute over the rule of law opposing Warsaw and Brussels after the European Court of Justice ruled earlier this year that the country's mechanism to discipline judges would violate EU rules and ordered its suspension.
Paris and Berlin backed Brussels late on Friday in a joint statement in which they affirmed that "membership of the European Union goes hand in hand with full and unconditional adherence to common values and rules."
"Compliance with these is the responsibility of each Member State and therefore, of course, also of Poland, which occupies a key position in the European Union.
"This is not only a moral commitment. It is also a legal commitment," they went on, reiterating their "support for the European Commission in its capacity as guardian of the Treaties to ensure compliance with European law."
The statement by the French and German foreign ministers, respectively Jean-Yves Le Drian and Heiko Maas, came less than a day before Hungarian Prime Minister Viktor Orban signed a government resolution welcoming a Polish constitutional court ruling.
In the resolution, Hungary's government calls on EU institutions to respect the sovereignty of the bloc's 27 member countries, Orban's spokesman, Bertalan Havasi, told the Hungarian news agency MTI.
The Hungarian resolution states that the poor practices of EU institutions which disregard the principle of delegation of powers triggered the Polish court's consideration of the legal primacy issue.
“The primacy of EU law should only apply in areas where the EU has competence, and the framework for this is laid down in the EU’s founding treaties,” the Hungarian document says.
The resolution also states that EU institutions are obliged to respect the national identities of member states. National law-enforcement bodies, in particular constitutional courts and tribunals, have the right to examine the scope and limits of EU competences, it says.
Budapest, like Warsaw, has been engaged in a tussle with Brussels over legislation targeting LGBT people, independent media and civil society.
Back in Poland, former prime minister and main opposition leader, Donald Tusk has meanwhile called for Poels to take to the streets on Sunday to defend their country's membership of the 27-country bloc.
In a message on Twitter, the former EU Council president wrote: "We have to save Poland, no one will do it for us."
Meanwhile, a far-right activist called "all patriots who care about the sovereignty of our state" to join a counter-protest in Warsaw.