The Environmental Protection Agency late Monday announced that U.S. power plants will have to cut their carbon emissions by 32% from 2005 level over the next 15 years if they want to keep operating, setting a slightly more ambitious target than the 30% it initially proposed a year ago.

The rule will be the centerpiece of the Obama’s negotiating strategy as his administration tries to tie up a global deal on arresting climate change at a summit in Paris in December. It’s also a key part of the legacy that the president will look to bequeath as he leaves office in 2016.

However, it still faces huge opposition from influential Republicans in Congress, especially those representing districts with strong coal mining constituencies. Senate Majority Leader Mitch McConnell, has vowed to thwart what he calls Obama’s “War on Coal”, claiming that the plans will lead to higher electricity prices for consumers if power companies are forced to ditch it for more expensive fuel sources. His claims are partly backed up by findings from the Energy Information Administration, which said bills would rise by an average of 3%, all other things being equal, if the EPA’s draft rule were implemented.

McConnell has called on states to delay complying with the EPA’s demand that they draw up the plans for cutting emissions, but didn’t immediately respond to the EPA’s final rule last night. However, West Virginia Attorney General Patrick Morrisey gave a taste of what’s in store as the Administration tries to force through its plans.

“The final rule announced Monday blatantly disregards the rule of law and will severely harm West Virginia and the U.S. economy,” Morrisey said. “This rule represents the most far-reaching energy regulation in this nation’s history, drawn up by radical bureaucrats and based upon an obscure, rarely used provision of the Clean Air Act. We intend to challenge it in court vigorously.”

House Speaker John A. Boehner, meanwhile, called the plan “an expensive, arrogant insult to Americans who are struggling to make ends meet”–but he didn’t renew previous threats to disrupt the rest of Congress’s agenda in order to get the rule scrapped.

The EPA’s power to set such targets was confirmed by a Supreme Court ruling in 2007 in a split 5-4 ruling. But the political momentum for cutting emissions only picked up after Obama issued an executive order in 2013. Many doubt the new rule will stick if a Republican President is elected in 2016.

The plan’s supporters argue that it is needed to guarantee U.S. leadership in forging a global response to a global problem (China has already overtaken the U.S. as the world’s biggest source of carbon emissions and India is on course to do the same), and any solution has to target the power sector, which accounts for 31% of U.S. greenhouse gas emissions (and about 5% of global carbon emissions), according to EPA and International Energy Agency data.

EPA Administrator Gina McCarthy argued in a blog post Monday that the plan also has major public-health benefits, as it will cut pollution (the same rationale is also the driving force behind China’s plans to cut carbon emissions). She estimates a total of $45 billion in climate- and health-related benefits by 2030.

McCarthy pointed out that states still have plenty of latitude on how to apply the plan. Analysts said the administration is counting on the introduction of a cap on emissions acting as an incentive for the industry to set up a more comprehensive nationwide system for trading emissions rights, after the last such initiative was blocked in the Senate.