The European Union on Wednesday handed Poland a three-month deadline to reverse changes to its constitutional court to meet EU concerns over the rule of law and democracy.
The move is the second step in an unprecedented procedure which could eventually see Warsaw's voting rights suspended in the European council of ministers, the EU's most important decision-making body.
"We now invite the Polish authorities to take action to solve these concerns and inform the commission of the steps taken within three months," European Commission deputy president Frans Timmermans told reporters.
Among the demands by the commission, the executive arm of the 28-nation EU, are for the constitutional court rulings to be published.
"What we are saying is that if the constitutional tribunal is to function, then when it issues a ruling... it must be published," said Timmermans, a former Dutch foreign minister who has been locked in a tense six-month stand-off with Poland.
Poland's conservative Law and Justice (PiS) party swept to power late last year and immediately pushed through legislation which critics say paralysed the constitutional court.
It has also ramped up state control over public broadcasters, further straining relations with the EU which demands that all member states meet the same rule of law and democratic norms.
The commission launched an initial probe in January to see if the changes violated EU rules and warranted punitive measures.
It formally warned Poland on June 1 to reverse the changes so as to remove a "systemic threat" to the rule of law, but said Warsaw had still failed to address the concerns despite further legislative amendments.
"The fundamental concerns are still unresolved," Timmermans said, adding the court still did not have the full capacity to carry out a constitutional review.
"This adversely affects its integrity, stability and proper functioning, which is one of the essential safeguards of the rule of law in Poland," he said.
Speaking to reporters in Krakow ahead of Pope Francis's first visit to the country, Poland's Interior Minister Mariusz Blaszczak said he was "astonished by the European Commission's decision."
The commission "should instead support the member states. They should concentrate on the fight against terrorism," the minister said.
Without a satisfactory response in three months, the Commission, the European Parliament or a group of 10 member states can propose Poland be stripped of its voting rights in EU institutions if it is guilty of serious and persistent breaches of the rule of law.