The Trump administration has asked a federal appeals court to postpone ruling on the merits of President Barack Obama's sweeping plan to address climate change.
The request late on Tuesday came hours after President Donald Trump signed an executive order that seeks to roll back his predecessor's effort to curb carbon emissions.
The regulations - known as the Clean Power Plan - have been the subject of long-running legal challenges by mostly Republican-led states and industry groups that profit from burning coal.
The US Court of Appeals for the District of Columbia Circuit heard arguments in the case last year and could issue a ruling any time.
Environmental groups oppose any delay.
A ruling in favour of the Obama-era rules could help environmental groups battle Trump administration efforts to undo them.
"Because the rule is under agency review and may be significantly modified or rescinded through further rulemaking in accordance with the executive order, holding this case in abeyance is the most efficient and logical course of action here," lawyers for the Justice Department said in their motion.
A coalition of 16 mostly Democratic-led states and environmental groups involved in the legal case say they will oppose the administration's request for a delay.
A ruling in favour of the carbon restrictions from the DC appeals court could help blunt the Trump administration's efforts to undo them and put the issue before the US Supreme Court.
Rewriting the Clean Power Plan and other carbon-limiting federal regulations is likely to take years to complete and is expected to face legal challenges from big Democratic-leaning states as New York and California.
In a call with reporters, New York Attorney General Eric Schneiderman said presidents do not have legal authority to just do away with Environmental Protection Agency regulations with the stroke of a pen.
Mr Trump's executive order did not attempt to withdraw a key 2009 EPA ruling that greenhouse gases such as carbon dioxide endanger the public's health and welfare. The Trump administration is also bound by a 2007 Supreme Court ruling that requires the federal agency to regulate planet-warming carbon emissions.
"We're very confident that the EPA can't simply dismantle the Clean Power Plan and leave nothing in its place," said Mr Schneiderman, a Democrat. "We regret the fact that the president is trying to dial back history, but it's not going to happen."
Meanwhile, members of the conservative coalition that sued to stop Mr Obama's plan were already declaring a "monumental victory" for their side.
"President Trump's decisive action lets everyone know this unlawful, job-killing regulation will find no support in his administration," said West Virginia Attorney General Patrick Morrisey. "That's a tremendous relief for every coal miner and family that depends upon coal's success.