Poland intends to sue the EU over its planned implementation of a market stability reserve (MSR) for the EU emissions trading scheme (ETS).
The decision to start the mechanism in phase three (2013-20) of the cap-and-trade programme is illegal, it said.
The Polish government will file a lawsuit in the European Court of Justice over the decision by the European Parliament and EU Council to launch a reserve in 2019 to absorb some of the excess EU ETS allowances.
The instrument will limit EU ETS oversupply to 400mn-833mn allowances by capturing 12pc/yr of the excess, which stands at over 2.1bn.
But the start of the MSR in 2019 will "significantly change the legal framework" and functioning of the EU ETS in phase three, Poland said.
This is something "market participants had not expected when they were planning their investment and business decisions", it said.
Warsaw has argued that the decision on the MSR's start date violates earlier council conclusions and effectively increases EU emissions reduction goals beyond the region's international obligations.
It did not specify when it intends to file the lawsuit.
Poland has repeatedly resisted the commission's push for deeper EU greenhouse gas emissions cuts, fearing that the move will inflate the cost of coal and lignite-fired power generation and reduce the competitiveness of the manufacturing sector.
The country produces more than 85pc of its electricity from coal and lignite-fired plants.
