The Trump administration will abandon the Obama-era clean power plan aimed at reducing global warming, officials said.
Speaking in Kentucky on Monday, Scott Pruitt, the administrator of the Environmental Protection Agency, said he will sign a proposed rule on Tuesday "to withdraw the so-called clean power plan of the past administration".
The clean power plan aimed to restrict greenhouse gas emissions from coal-fired power plants.
It was a centrepiece of the Obama administration's environmental policies.
The Environmental Protection Agency is expected to declare the Obama-era rule exceeded federal law by setting emissions standards that power plants could not reasonably meet.
Mr Pruitt said the EPA should not use its authority "to say to you we are going to declare war on any sector of our economy".