The Obama administration proposed on Tuesday the first ever standards to cut carbon dioxide emissions from new power plants, a move likely to be hotly contested by Republicans and industry in an election year.
The Environmental Protection Agency proposed the long-delayed rules that limit emissions from all new U.S. power stations, which would effectively bar the building of any new coal plants.
While the rules do not dictate which fuels a plant can burn, they would require any new coal plants essentially to halve carbon dioxide emissions to match those of efficient gas plants.
"We're putting in place a standard that relies on the use of clean, American made technology to tackle a challenge that we can't leave to our kids and grandkids," EPA Administrator Lisa Jackson said in a release.
Republicans have already turned to the courts to forestall other EPA measures they say will drive up power costs for homeowners and businesses that are struggling to recover from the weak economy. Some Democrats from energy-intensive states are also likely to oppose the rules.
The EPA's overall clean-air efforts have divided the power industry between companies that have moved toward cleaner energy, such as Exelon and NextEra, and those that generate most of their power from coal, such as Southern Co and American Electric Power.
Under the rules, coal plants could add equipment to capture and bury underground for permanent storage their carbon emissions. The rules would likely give any new coal plants time to get those systems running, by requiring that they average the emissions cuts over decades.
Supporters of the rules argue that the industry has been moving away from coal and towards natural gas because of low prices and abundant supply. The portion of U.S. electricity fired by coal has slipped from about 50 percent to 45 percent in the last few years as hydraulic fracturing, or fracking, and other drilling techniques have allowed access to vast new domestic supplies of natural gas.
The EPA is moving forward on the climate rules, which do not need to be approved by Congress, after a wide-ranging climate bill died in the Senate in 2010.
The EPA is the main tool the Obama administration has left to reduce greenhouse gas emissions and meet goals agreed at global forums to battle climate change.
But the agency's moves are also met by challenges by industry in the courts and have been under withering criticism from Republicans, who have made environmental regulations a big campaign theme ahead of the November elections.
The green movement is key part of President Barack Obama's base and the administration has tried to walk a tightrope with its "all of the above" energy strategy that includes tougher energy regulations and support for renewable energy.
Environmentalists who were stung by Obama's decision last September to delay a major smog rule, cheered the prospect of performance standard rules they say will help protect the country from climate change.
"The bottom line for our country is that cleaner power will cut harmful carbon dioxide pollution, protect our children and help secure a safe prosperous future," said Vickie Patton, the general counsel for the Environmental Defense Fund.
The rules are expected to affect only new plants, not modified plants, which would be a concession to industry. Existing plants would not be included, but the new proposals could set the stage for the EPA to regulate them in the coming years.
The EPA's clean-air chief Gina McCarthy has said there is no guarantee the rules will be finalized before the November 6 election, which means they could be more easily overturned if Obama lost the election.