Power plants are the nation's largest source of carbon pollution, accounting for about 30 percent of its greenhouse-gas emissions.
The bulk of the emissions are from coal-fired power plants, making them a target, but they also provide 40 percent of the nation's electricity.
Pennsylvania - a major power producer and coal state - promises to figure large in the debate.
Details of the plan were first reported Sunday by the Wall Street Journal.
The draft rule, one more in a suite of regulations aimed at coal-plant emissions, has already rankled industry, which warns of higher electric costs and a less reliable power grid.
"Of course, everyone would like to see, and we envision a future with, cleaner air and a stronger economy, but the regulations are . . . pushing too far too fast," said Nancy Gravatt, a spokeswoman for the National Mining Association.
Meanwhile, environmental groups, public-health officials, and others supportive of the action have been rallying for a strong rule by issuing analyses and public survey results.
"This action is long overdue," said Janice Nolen, an American Lung Association policy expert.
The rule "will improve the health of our kids and our communities," said Daniel Lashof, a senior fellow with the Natural Resources Defense Council. "As it turns out, it will also be good for our economy."
Either way, "the rule is going to be challenged in court, regardless," predicted Brendan Collins, an environmental lawyer at the Philadelphia firm Ballard Spahr L.L.C. who has expertise in the climate-change and environment sector.
Environmentalists will sue if it is too weak; industry will if it is too aggressive, he said before details were disclosed. "There's no Goldilocks solution."
Other countries - especially China - will be watching closely to see if the United States is serious about cutting greenhouse-gas emissions, analysts say.
Pennsylvania's power generators also are on alert, said Jake Smeltz, president of the Electric Power Generation Association, a Pennsylvania industry group.
The state is a power powerhouse, the No. 1 exporter of electricity in the nation. In actual production of electricity, only Texas makes more. Also, the state ranks fourth in coal production.
"We believe that there is very much value in having industries like electric power generation in the state," Smeltz said. "We're manufacturers. We just happen to make electrons."
A March report commissioned by the coal industry found it provided 36,187 jobs and contributed $4.1 billion in economic impact in Pennsylvania.
The industry has accused the administration of mounting a war on coal. The website home page of the Pennsylvania Coal Alliance shows a rippling American flag and urges, "Join the fight."
CEO John Pippy contends the rules aren't about improving coal technologies but eliminating coal as a fuel source altogether. "There are a lot of reasons we're concerned," he said.
Earlier EPA rules have prompted plant closures in Pennsylvania.
According to an analysis by the Sierra Club's Beyond Coal campaign, eight of the state's 33 plants have been retired, two have announced plans to be retired, and two are switching to natural gas. The closing plants represent nearly 30 percent of coal-plant capacity in the state, the group says.
Countering claims that the state's economy could be bruised by the new rules, Beyond Coal's state campaign representative, Tom Schuster, said families and businesses already were subject to "the dramatic effects of climate disruption," such as heat waves, floods, and droughts.
Smeltz would like to see the state get credit for carbon dioxide reductions already achieved by the plant closures.
Its geriatric fleet of coal-fired power plants notwithstanding, Pennsylvania is already well-positioned to meet emissions-reduction targets, according to a recent World Resources Institute analysis.
If the state expands its clean-energy technologies, it will be "in a good position in the near term to comply with moderately ambitious standards," said the Institute's Michael Obeiter.
"I don't think it's this death knell" for coal-fired power plants, said Christina Simeone, an energy expert with the state environmental group PennFuture. "It's an approach to modernizing our power system."
Even before details of the rule were announced, the National Mining Association began running radio and digital ads in Pennsylvania and four other states that it ranks as key because they have a strong manufacturing base - meaning lots of electricity use - and make lots of coal-based energy.
It begins with people opening their electric bills and gasping: "We can't afford this." An 80 percent hike - vigorously challenged by others - is something people should get used to "if the extreme new Obama administration power-plant regulations take effect," the narrator says.
Environmental groups are ramping up their own campaigns. PennEnvironment has hired 12 new organizers in Pennsylvania alone, plus others in North Carolina and Colorado, in part "to fight back against misleading ads from the coal industry," said field director Adam Garber.