Supporters contend the rules are necessary to help address climate change; opponents argue that the new rules will harm the economy and affect the reliability of the U.S. electric grid.

The same day the rules were published, 24 states and a handful of industry and business groups, including the U.S. Chamber of Commerce, filed lawsuits in the D.C. circuit court of appeals, challenging the rule for existing plants.  Several of the same groups also requested a stay of the Dec. 15 effective date until the court makes a decision on the case. EPA immediately filed an emergency motion to delay a ruling on whether to grant the opponents’ request. However, on Oct. 29, the court said it would hold off on making a decision until after the mid-December Paris climate talks.

EPA’s rule would require states to develop plans to reduce carbon emissions from existing powerplants. Most of the lawsuits argue that the rule exceeds EPA’s Clean Air Act authority.

Political observers say they expect the litigation to go to the U.S. Supreme Court and could take years to resolve. Meanwhile, lawmakers in both the House and Senate are expected to vote before Thanksgiving on legislation to permanently repeal the rules. Forty-eight senators are co-sponsoring a so-called congressional resolution of disapproval to block the rule for new powerplants; 49 have signed on to a bill opposing the rule for existing powerplants. But the resolutions would face an almost certain presidential veto.