The European Commission laid out its options - ranging from legal action to withholding funds - for a response to a Polish court ruling that questioned the supremacy of EU law, stressing that action must be taken to protect the bloc's common values.

"The European Commission is, at the moment, carefully assessing this judgment," the European Union's executive president, Ursula von der Leyen, said on Tuesday.

"But I can already tell you: I am deeply concerned," she told the European Parliament in Strasbourg ahead of a speech to the assembly by Polish Prime Minister Mateusz Morawiecki.

"This ruling calls into question the foundations of the European Union. It is a direct challenge to the unity of the European legal order."

She said a first option is so-called infringements, where the European Commission legally challenges the judgment by the Polish Constitutional Court.

Another option is a conditionality mechanism and other financial tools whereby funds from the EU's budget and its post-pandemic recovery fund would be withheld from Poland.

"This is European taxpayers' money. And if our Union is investing more than ever to advance our collective recovery, we must protect the Union budget against breaches of the rule of law," von der Leyen said.

She said a third option is the application of Article 7 of the EU's treaties under which rights of member states - including the right to vote on EU decisions - can be suspended because they have breached core values of the bloc.

"The Polish Constitutional Court that today has cast doubts on the validity of our Treaty is the same court that under Article 7 we consider not to be independent and legitimate," she said. "This comes in many ways full circle."