Opponents of the Obama administration’s Clean Power Plan are pointing to the recent Supreme Court decision rejecting the EPA’s mercury regulation as a prime example of why Congress or the judicial branch should preclude implementation of the agency’s climate rules’ while they’re challenged in court.

Industry and coal-heavy states got a win on paper at the high court, with justices ruling 5-4 on June 29 that the agency improperly ignored cost considerations when deciding to regulate mercury emissions from power plants. But the rule’s impact has already been felt; since it went into effect in April, nearly two-thirds of the affected plants have complied without seeking extensions, according to the National Association of Clean Air Agencies.

Lawmakers are already citing the outcome as a cautionary tale heading into a multi-year challenge to the EPA’s carbon pollution limits on new and existing power plants. The rules are expected to be finalized this summer. The limited practical effect of the Supreme Court decision on mercury, which will require the EPA to, at minimum, revise part of its rule, gives opponents ammunition to press for states to not have to comply with the climate regulations until judges decide their fate.

The EPA’s carbon rules would set state- specific carbon-reduction goals. Utilities would strive to meet them by switching from coal to cleaner-burning fuels.

“While much of the damage of this regulation has already been done, the ruling serves as a critical reminder to every governor contemplating the administration’s demands to impose more regressive — and likely illegal — regulations that promise even more middle-class pain,” Senate Majority Leader Mitch McConnell said in a statement. “Clearly, there is no reason to subject their states to such unnecessary pain before the courts have even had a chance to weigh in, especially if the Supreme Court simply ends up tossing the regulation out as we saw today.”

Industry groups and states that are likely to sue the EPA over the Clean Power Plan will likely point to the mercury regulation’s impact on coal-fired plants when pushing for a stay of the climate rules while the court process plays out.

The mercury rule “is a pretty egregious example of a case where a lot of things have happened that really are, you know, irreversible because the rule stayed in effect during the litigation,” said Jeff Holmstead, an EPA air official during the George W. Bush administration who now lobbies for utilities.

“I think that it really does help folks who are not only going to be challenging the Clean Power Plan, but asking the courts to stay it during the litigation,” he added.

Congressional Republicans and coal-state Democrats are pushing for a stay legislatively. The House passed a bill (HR 2042) last week to allow states to delay implementing the carbon limits on existing plants until the courts decide on their legality. The legislation also permits states to avoid compliance entirely if they find the rule would negatively affect electric reliability and rates.

“Unfortunately, this ruling comes after the rule has already [taken] a toll, with a number of power plants shuttered and many jobs lost because of the EPA’s unlawful action,” House Energy and Commerce Chairman Fred Upton, R-Mich., and Energy and Power Subcommittee Chairman Edward Whitfield, R-Ky., said in a joint statement. “The ruling further underscores the need to extend the compliance requirements for the pending [existing plant] rule until the numerous legal questions surrounding it are fully resolved.”

The White House threatened to veto the measure, and officials have made it clear Obama has no plans to forsake regulations he views as the cornerstone of his legacy on climate change. All eyes then will be on the federal appeals court when it eventually considers lawsuits against the standards.

A stay of the regulation pending review is “not common, but it’s not unprecedented either,” Holmstead said. The U.S. Court of Appeals for the D.C. Circuit paused implementation of the EPA’s cross-state air pollution rule until after the Supreme Court upheld the agency’s approach to regulating toxic emissions that blow across state lines last year.

A Clean Power Plan delay likely wouldn’t have much effect in states that have already taken steps to cut carbon emissions and are inclined to seek further reductions. To be sure, many states run by governors who oppose the rule are still working on implementation plans to ensure that they have some strategy for emissions reductions as the regulation’s future is decided.

But a stay would likely help coal-dependent states that have already voiced intense opposition to the rule slow-walk any major cuts to their carbon footprints. And any hiccup could significantly impact the U.S. pledge to the United Nations to reduce carbon pollution by at least 26 percent below 2005 levels by 2025 — a target that’s predicated on using existing laws and authorities to achieve climate goals.