The Supreme Court’s conservatives expressed skepticism over the Biden administration’s efforts to reduce smog and air pollution wafting across state lines during arguments Wednesday in the most significant environmental dispute at the high court this year.

Three Republican-led states, industry groups and electric utilities want the justices to temporarily halt the Environmental Protection Agency’s “good neighbor” plan, which imposes strict emission limits on power plants and other industries in upwind states.

Several of the court’s conservative justices noted that the EPA plan, which originally dealt with 23 upwind states, now applies to only 11 because of a series of lower court rulings that sided with states opposed to the effort.

Justice Brett Kavanaugh said the EPA decided to “plow ahead anyway” even when it became clear that the plan would likely not apply to some states.

He characterized the agency’s response as “pretend nothing happened.”

“I agree with you about the equities of the downwind states,” Kavanaugh told the lawyer representing the Biden administration, referencing the potential for pollution that crosses into their states, “but there’s also the equities of the upwind states and the industry. They’re both major.”

Ohio, Indiana and West Virginia filed the emergency request with the Supreme Court in October, claiming the EPA overstepped its authority by imposing those requirements. They also argued the plan – and the original justification for it – were undermined by court decisions halting its application in many states.

The Biden administration and other states led by New York and Connecticut have warned of “dangerous ozone spikes” affecting the health of residents – particularly children and the elderly – if the court sides with their upwind neighbors.

The Supreme Court must decide whether to temporarily block the EPA effort while the underlying legal fight continues. Because the case began on the court’s emergency docket, a decision could be reached relatively quickly.

In broad terms, the combined cases are among several this year in which the Supreme Court is being asked to weigh the power of federal agencies to impose regulations. Environmental groups have been dealt a series of significant losses by the court’s conservatives, including a decision in 2022 that limited the EPA’s ability to regulate carbon emissions from power plants.

The three liberal justices hammered the lawyers representing the conservative states and industry groups, questioning whether the Supreme Court should grant the request to halt the plan given that lower courts have not finished deciding the case.

“If we’re going to entertain every motion that someone has about being harmed, or whatnot, in the lower courts before any of the lower courts even get the opportunity to talk about it – I feel like we have to have something that guides our consideration of when to do that,” said Justice Ketanji Brown Jackson.

The Clean Air Act requires the EPA to occasionally review interstate pollution rules to ensure they align with the latest health guidelines. The Obama administration updated the standards in 2015 and states were required to submit plans within three years showing how they would meet the new goals.

But the Biden administration said the plans submitted by 21 states included “no action to assist downwind neighbors” and that two states failed to submit plans altogether. And so, last year, the EPA rejected those proposals and crafted its own plan for the 23 states. That included requirements that power plants install technologies the administration says are “widely adopted across the industry” to reduce nitrogen-oxide emissions.

“Polluting industries always challenge pollution regulations because it costs them money to protect our health,” said Sam Sankar, senior vice president of Earthjustice, one of the groups defending the plan. “We’re hoping that a few members of the court’s right-wing supermajority will remember that they shouldn’t be second-guessing sound judgments about what’s best for our kids’ lungs.”

And that’s when the dispute got even more complicated: Several states sued the EPA in separate litigation and multiple courts of appeal blocked the steps taken by the federal government in a dozen states. That left the EPA’s plan in effect in only 11 of the 23 states that were originally supposed to be covered by it.

Critics of the EPA’s plan say the uncertainty about its application underscores the problem with the administration’s approach. The Republican states told the Supreme Court that the federal plan is “down to a sliver” of what the agency initially intended. Those failures, the states argue, “were both foreseeable and inevitable.”

Those opposing the EPA have also warned the plan could “destabilize the states’ power grids.” The Biden administration says such predictions are based on “speculative allegations” that some power plants may be required to shut down “at some future point.”

The “good neighbor” plan would be “massively harmful to industry and consumers,” said Tawny Bridgeford, general counsel for the National Mining Association, which opposes the regulations. “We’re hopeful that the Supreme Court will recognize the unlawful overreach represented in this rule.”

The DC Circuit declined to temporarily block the plan while the underlying legal fights continue. The states and industry groups opposing the EPA then asked the Supreme Court for an emergency order to freeze the plan’s implementation. In December, the court took the unusual step of agreeing to hear arguments solely on whether the plan should be paused.

It’s only the third time since 1971 that the court has heard arguments on an emergency request, said Steve Vladeck, CNN Supreme Court analyst and professor at the University of Texas School of Law.