EPA chief Scott Pruitt has made fast work of implementing a deregulatory agenda in the six months since he took his post, but the wide-ranging impact of a court decision issued late Monday could force him to downshift dramatically.

A panel of judges on the U.S. Court of Appeals for the D.C. Circuit Court delivered a blow to Pruitt’s agenda Monday, forcing the EPA to implement an Obama-era methane rule that, under Pruitt, it had tried to delay. The decision indicates one of the main deregulatory tactics that Pruitt’s EPA has employed — delaying the implementation of Obama-era rules long enough to gut them — can be successfully challenged in the courts.

In the case of the methane rule, the agency is still considering a two-year stay on its implementation. The agency is holding the comment period and will try again to get the rule stayed, but Monday’s ruling made clear the courts are not playing ball with its delay tactics.

It’s currently the EPA’s most effective maneuver, and the agency has used it to sandbag a rule that imposed tighter safety rules on the oil, gas, and chemical industries and to enact a 90-day stay on a rule that regulates methane emissions from landfills. Both are the subject of legal actions. And the EPA’s promised replacement for Obama’s Clean Water Rule, which has been stayed since 2015, will likely come before the courts as well.

The breakneck pace at which the EPA has rolled back rules is likely slow as more courts grapple with the issue. The ruling could also have implications for the wider deregulatory agenda that President Trump’s been pursuing — not just at the EPA, but across all agencies.

“The Trump administration has been much more aggressive at trying to pull back rules by trying to extend their effective date than either the Obama or Bush administrations before them,” says Thomas McGarity, environmental law professor at the University of Texas at Austin.

Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia University, says the case, on its face, affects the EPA’s ability to delay rules that have already gone through the public comment process. But he says it also sets an important precedent: “It’s a new assertion of executive authority. Yes, this about the methane rule, but what we’re seeing here is an effort to undermine the legitimacy of the administrative state altogether.”

The D.C. Circuit Court acted quickly in rejecting the EPA’s move to stay the methane rule, issuing two rulings in the month since the EPA tried to delay implementing the methane rule — the first, on July 3, calling a shorter, 90-day stay on the rule illegal, and the second on July 31, in which nine of 11 judges voted decisively to force the EPA to enforce the rule.

The methane rule is an Obama-era regulation aimed at keeping methane emissions low at new oil and natural gas drilling sites, primarily by forcing the oil and gas industry to plug up leaks in their wells. The EPA, at the time, found that following the rule would both increase the efficiency of natural gas drilling and help curb air pollution.

Fracking, in particular, leaks a lot of methane into the air, and methane is a very potent greenhouse gas: It traps over thirty times more heat than carbon dioxide, according to the UN’s Intergovernmental Panel on Climate Change.