A separate rule limiting the emissions of mercury and other toxins was made final earlier in December and will start requiring emissions cuts in 2015. According to The Wall St. Journal, the cross-state rule would have required pollution reductions in 2012. To comply, companies with older coal-fired power plants would have had to run those plants less often or pay for credits to offset the pollution. Those facilities will still have to control some pollution, because the court said a Bush-era version of the rule would remain in effect. The EPA’s new version was stricter.

In an unsigned order, a three-judge panel said it would hear the case by April.

Power companies and state regulators challenged the rule this fall on the basis that, among other things, the agency didn’t give power generators enough notice and it made significant errors in its calculations regarding costs. Others argued that the law over-reached on a state’s ability to determine its pollution-control plans, as the Clean Air Act requires.