The Supreme Court on Thursday temporarily blocked a rule issued by the Environmental Protection Agency to reduce air pollution from power plants and other industrial facilities in 23 states. By a vote of 5-4, the justices granted a request from three states, as well as several companies and trade associations affected by the rule, to put the rule on hold while a challenge to it continues in a federal appeals court in Washington, D.C.

Justice Neil Gorsuch, whose mother Anne Burford McGill served as the head of the EPA during the Reagan administration, wrote for the majority.

Thursday’s ruling came in one of the relatively rare disputes to come to the Supreme Court through its emergency appeals – or “shadow” – docket. It stems from the EPA’s interpretation of a law known as the “good neighbor” provision of the Clean Air Act, which requires “upwind” states to reduce emissions that affect the air quality in “downwind” states.

Nearly a decade ago, the EPA issued new air-quality standards for ozone pollution, which can cause major health problems when it is present at high levels. The issuance of the new standards triggered an obligation for states to submit plans in which they indicated both how they would comply with the new standards and how they would reduce emissions affecting the air quality in downwind states.

In 2023, the EPA rejected plans submitted by 21 states, which had not proposed any changes to their emissions plans. The EPA then published its own plan that would cover those 21 states as well as two more states that had not submitted plans.

Three of those states – Ohio, Indiana, and Virginia – went to the U.S. Court of Appeals for the District of Columbia Circuit to challenge the EPA’s plan, as did several companies and trade associations. That court declined to put the plan on hold while litigation continued, prompting the challengers to ask the Supreme Court to intervene. In December, the justices agreed to fast-track the case for oral argument in February.

In an opinion by Gorsuch that was joined by Chief Justice John Roberts and Justices Clarence Thomas, Samuel Alito, and Brett Kavanaugh, the court granted the challengers’ request to put the plan on hold for now.

Gorsuch explained that allowing the plan to remain in place would affect both sides of the dispute. He acknowledged that the plan would improve the air quality in “downwind” states. But on the other hand, he continued, if the EPA did not act properly in adopting the plan, it would infringe on the states’ interests “in regulating their own industries and citizens.” Moreover, he continued, requiring the challengers to comply with the plan while litigation continues could cost them “hundreds of millions, if not billions of dollars.”

Given the considerations on both sides of the debate, Gorsuch continued, the key question in deciding whether to put the plan on hold temporarily is whether the challengers are ultimately likely to prevail on their argument that the plan is flawed. Here, Gorsuch reasoned, the scale tips in favor of the challengers, because the EPA did not explain why the emissions-control measures required by the plan – which were based on the assumption that the plan would apply to all 23 states – should still apply even if (as eventually happened) fewer states remained in the plan.

Justice Amy Coney Barrett penned a dissent that was joined by Justices Sonia Sotomayor, Elena Kagan, and Ketanji Brown Jackson. She criticized the majority for blocking enforcement of the EPA’s plan “based on an underdeveloped theory that is unlikely to succeed on the merits.” Although skeptical about whether, for procedural reasons, the challengers could even bring their lawsuit, she contended that the EPA had provided a sufficient explanation for the plan to survive. “EPA,” she wrote, “would have promulgated the same plan even if fewer States were covered.”

But more broadly, Barrett complained, “the Court’s injunction leaves large swaths of upwind States free to keep contributing significantly to their downwind neighbors’ ozone problems for the next several years.” And the court “justifies this decision based on an alleged procedural error that likely had no impact on the plan.”

Shortly after the court’s decision, Sam Sankar – a senior vice president at the environmental group Earthjustice – cautioned that the ruling could lead to more industry challenges to new environmental rules. But he added that the case will continue in the D.C. Circuit, which could hear oral argument on the merits of the dispute as soon as this fall.

This post is also published on SCOTUSblog.