Polish Prime Minister Mateusz Morawiecki accused the EU of "blackmail" on Tuesday in a public clash with European Commission chief Ursula von der Leyen over his country's rejection of parts of EU law.
The row, played out in the European Parliament, underlined the seriousness of the issue which both Brussels and Warsaw say threatens the cohesion of the 27-nation bloc.
"We cannot and we will not allow our common values to be put at risk," she said, enumerating legal, financial and political options being considered.
Morawiecki, in a speech running over his allotted time, hit back by saying "it is unacceptable to talk about financial penalties... I will not have EU politicians blackmail Poland."
A ruling by the Polish Constitutional Court on October 7 questioning parts of EU law ratcheted up tensions with Brussels that have been festering for years.
The European Commission and European Parliament have taken Warsaw to task for moves to scrap judges' independence and other policies seen as rolling back democratic norms.
They have also criticised Poland for ultraconservative social policies pushed by the ruling Law and Justice (PiS) party restricting LGBTQ rights and placing a near-total ban on abortions.
Analysts said the ruling partially rejecting the supremacy of EU law could be a first step towards Poland one day leaving the European Union.
But Morawiecki insisted that Poland's place was in the EU and that EU law derived from its treaties only applied in specified areas, with Poland's national constitution supreme in all other aspects.
Tens of thousands of Poles rallied this month to declare their strong desire to remain in the European Union.
One of the measures the Commission could use against Poland is withholding recovery cash from a pooled EU fund set up for the bloc to bounce back from the impact of the coronavirus pandemic.
Poland's plan, asking for 23 billion euros ($27 billion) in grants and 34 billion euros in cheap loans, is still being weighed, with the Commission saying approval would come with strings attached.
Morawiecki, in a letter released on Monday, said that amounted to "financial blackmail, punishment, 'starving' of unsubordinated states".
In return, Poland has the power to play spoiler in several key EU policy areas that require unanimity among the 27 countries, among them its stance on fighting climate change and migration.
It also has the support of Hungary, another bête noire for Brussels seen to be flouting rule of law.
The leaders of the EU are to hold a summit in Brussels on Thursday and Friday. The wrangling over Poland could move up its agenda, with the Netherlands and Luxembourg especially critical of Warsaw.
As he went into a preparatory meeting of EU European affairs ministers on Tuesday, Luxembourg's Foreign Minister Jean Asselborn told AFP: "Europe will not survive if rule of law falls. That's very clear."
The EU justice commissioner, Didier Reynders, also attending the meeting in Luxembourg, said the Commission was "very concerned" about the row with Poland and stressed the "binding character" of EU law on member states.
"We will continue to debate the (Polish recovery) plan," he said, linking it to Poland's judicial reforms.
"There must be both investments and reforms, and these reforms go to the independence of the courts, and so we are waiting for a very clear message on this topic," he said.
In Strasbourg, von der Leyen said that "I deeply regret that we find ourselves in this situation."
She added: "This is a situation that can and must be resolved.... Poland has a stake in Europe."