Relations between Brussels and Warsaw have been strained since the Law and Justice party (PiS) returned to power in Poland in October.
The European Union puts a defiant Poland in the dock on Wednesday over changes to the state media and constitution, in a move which could expose Warsaw to punitive measures for breaching democratic standards.
The European Commission, the executive arm of the EU, will hold a formal debate on an issue which has strained relations with the new right-wing government of one of the 28-nation bloc's largest members.
Poland has hit back strongly by accusing Brussels of attempting to pressure its government, while a Polish magazine depicted EU leaders including German Chancellor Angela Merkel in Nazi uniforms.
Polish Justice Minister Zbigniew Ziobro said on Tuesday he was "astonished" by letters from Brussels, slamming them as "an attempt to exert pressure upon the democratically elected" parliament and government of a sovereign state.
Relations between Brussels and Warsaw have been strained since the Law and Justice party (PiS), led by the eurosceptic Jaroslaw Kaczynski, returned to power in Poland in October after eight years in opposition.
The row erupted in late December when EU Commission Vice President Frans Timmermans sent Warsaw two letters seeking explanations about the party's moves to enact legislation giving it control over Poland's top court and public broadcasters.
Germany's European Commissioner Gunther Oettinger also threatened to put Poland on notice over the media law, while the German head of the European Parliament, Martin Schulz, has also criticised the Polish government.
The European Commission then announced that it would hold Wednesday's "orientation debate", invoking its "Rule of Law mechanism", which gives Brussels the power to discipline member states found to have subverted EU rights standards.
Offending states can ultimately be stripped of their EU voting rights -- the so-called "nuclear option" -- although this has never happened before.
'Not bashing Poland'
EU officials insisted that any rule of law procedure could not be launched at Wednesday's debate, but only afterwards, if necessary.
"It is the first opportunity for commissioners to debate at political level on the basis of the latest information presented by Timmermans," one European official told AFP, asking not to be named.
"Such a debate could then lead (or not) to a decision to activate for the first time the rule of law framework. But this is not for Wednesday," the official said.
The split is the latest to emerge in a European Union that has been deeply divided by a series of problems ranging from Greece's near exit from the euro currency to the continent's biggest migration crisis since World War II.
Poland's new government is also upending years in which Warsaw has built an influential position in Brussels, with former centrist Polish premier Donald Tusk now the president of the European Council, which groups the 28 EU leaders.
The new Polish government has found common cause with Hungarian Prime Minister Viktor Orban, who has likewise fallen foul of the Commission over his changes to the judiciary and press.
On Thursday, Poland's PiS-backed President Andrzej Duda signed into law a bill giving the government direct control of public broadcasters.
Warsaw insists the new measures are necessary for an impartial state media and constitutional court, and accused the previous centrist government of having tried to bring the institutions under its own influence.
Brussels has meanwhile tried to play down the issue, even as it pushes on with the debate.
"Let's not overdramatise," European Commission chief Jean-Claude Juncker said last week. "Our approach is very constructive -- we are not bashing Poland."
President Duda will be in Brussels next week for what Polish officials say is a long-planned and unrelated visit for talks with Tusk and NATO chief Jens Stoltenberg.