The Trump administration is moving ahead with a plan to roll back an Obama administration rule designed to curb power plants’ greenhouse gas emissions.
Environmental Protection Agency (EPA) Administrator Scott Pruitt, who has cast doubt on climate change, said the Clean Power Plan was an overreach.
President Donald Trump ordered the EPA to rewrite the rule in March.
The Clean Power Plan requires states to meet carbon emission reduction targets based on their energy consumption.
Mr Pruitt said he would sign the proposed rule to begin withdrawing from the plan on Tuesday.
“The war on coal is over,” he told a crowd in Hazard, Kentucky, on Monday.
He continued: “That rule really was about picking winners and losers.
“Regulatory power should not be used by any regulatory body to pick winners and losers.”
Mr Pruitt has previously argued that the Clean Power Plan would force states to favour renewable energy in the electricity-generation market.
As Oklahoma’s attorney general, he took part in a lawsuit by 27 US states against the rule.
A Supreme Court ruling in February 2016 left the regulation in limbo.
The EPA under President Barack Obama said the Clean Power Plan could prevent up to 150,000 asthma attacks in children and 6,600 premature deaths.
But according to US media, a leaked draft of the repeal proposal disputes the health benefits touted by the previous administration.
The draft also reportedly argues the country would save $33bn (£25bn) by dropping the regulation.
The Clean Power Plan required states to devise a way to cut planet-warming emissions by 32% below 2005 levels by 2030.