While the majority of interested parties are watching the legal fight over the U.S. Environmental Protection Agency's Clean Power Plan, challenges against the agency's rule capping carbon emissions from new power plants could serve as a proxy, delaying or derailing implementation of the plan's carbon limits on existing plants.

The new plant rule, which was crafted under the Clean Air Act and includes emissions caps for new coal-fired and both new and reconstructed gas-fired plants, is much less controversial than the Clean Power Plan because the abundance of cheap natural gas has made constructing new coal-fired plants uneconomical.

Regardless, coal giant Murray Energy Corp. and dozens of states have petitioned the D.C. Circuit to block the EPA’s new plant rule, saying the agency is overstepping its authority under the CAA.

“Part of the litigation has to be regarded as merely another front in the war against the Clean Power Plan,” said Ballard Spahr LLP environmental partner Brendan Collins.

That position is that under the CAA, the EPA can issue rules addressing emissions only from existing sources after it has issued rules addressing emissions from new sources.

Besides, whether an emissions reduction technology is feasible is ultimately a technical judgment, which works in the EPA's favor when the agency's rules are challenged in court, Collins said.

“The D.C. Circuit and most courts are loath to override to what is fairly characterized as a technical judgment by EPA,” Collins said. “Generally, cases that have gone against EPA are over statutory interpretation.”