The heart of the issue is whether Poland's populist and nationalist Law and Justice party is taking an authoritarian turn and eroding democratic institutions. The focus of concerns has centered largely on the independence of Poland's Constitutional Tribunal but also on other issues perceived as backsliding on fundamental political rights.
The government stands by its democratic credentials and says that street protests and the opposition's occupation of parliament are attempts at destabilizing the state.
EU Vice-President Frans Timmermans weighed in on Wednesday, voicing renewed concerns over respect for the rule of law in Poland. He said he has sent a series of recommendations and given the Polish government two months to reply.
Timmermans said the 28-nation bloc "will not drop this matter."
"We feel a strong, strong feeling of solidarity with the Polish people who deserve, like all Europeans, to have an independent judiciary, to have a full separation of powers," Timmermans said.
Government spokesman Rafal Bochenek described the latest EU step as unnecessary. He said the government has solved its issues with the constitutional court, citing a new law regulating the court and the swearing in Wednesday of a new court president chosen by the ruling party.
Poland has been in a state of political tension since Law and Justice assumed power in November 2015 and moved quickly to solidify control over state institutions.
Tensions spiked last Friday over a plan by the ruling party to restrict media access in parliament. Opposition lawmakers began a sit-in around the speaker's podium that blocked proceedings on the budget. Large street protests also erupted and lasted for days.
The ruling authorities have since backed away from that media plan, but a dispute continues from that sit-in - a vote on the 2017 budget that ruling party lawmakers held in a separate room. Opposition lawmakers say that vote violated parliamentary procedures and must be held again.
Grzegorz Schetyna, head of the opposition Civic Platform party, said protesting lawmakers will remain inside parliament's main assembly hall in protest until Jan. 11, when parliament is to resume after a holiday break.
Law and Justice party chief Jaroslaw Kaczynski called the behavior of opposition lawmakers of a "criminal nature" and appealed to them to respect the law.
In reaction to the protests in Warsaw, state authorities have increased security outside of parliament, erecting metal barriers. Dozens of protesters gathered there Wednesday afternoon, vowing to remain as long as the protest inside the building continues.
"We will stay here til Jan. 11 to support the lawmakers, because they are fighting for us, for Polish society, so that we have full rights like in any democracy," said Elzbieta Grudzinska, an architect who has spent several nights there since Friday.
Raf Casert in Brussels and Monika Scislowska in Warsaw contributed to this report.
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