By overturning Chevron deference, the justices took power away from agencies regulating everything from health care to pollution.

In one of the most highly anticipated decisions this term, the Supreme Court overturned a 40-year-old legal doctrine, so-called “Chevron deference,” under which judges had been expected to defer to a federal agency’s interpretation of laws that are ambiguous. The ruling, split 6-3 along ideological lines, will have far-reaching consequences, experts say, and could impact all sorts of federal policies, from health care and taxes to climate change.

The cases at the center of this decision—Relentless, Inc. v. Department of Commerce and Loper Bright Enterprises v. Raimondo—on their most basic level, involve a dispute about herring fishing and regulatory fees. In an effort to prevent overfishing, the federal government required fishers to pay at least some of the cost for legally mandated monitors to observe their fishing operations. The fishermen behind the cases—backed by anti-regulatory interests like Charles Koch—argued that they shouldn’t have to foot the bill because the law doesn’t specify who pays.

But this ruling is much, much bigger than a fight over fishing fees. Vickie Patton, general counsel for the Environmental Defense Fund, whom I spoke to in advance of the ruling, sees the challenge to Chevron deference (named after a 1984 Supreme Court case, Chevron U.S.A. v. Natural Resources Defense Council) as part of an “extensive campaign” by industry and their allies to unravel federal authority to regulate food safety, clean air, clean water, protections from consumer fraud, and more. “The stakes for people’s lives are profound,” she said.

“Profound” is right: Chevron is among the legal field’s most cited doctrines ever. That’s because ambiguity is everywhere in policy-making. And in legal disputes over ambiguous statutes, Chevron says judges, within reason, ought to defer to federal agencies’ understanding of those statutes.

In this case, the law in question was the 1976 Magnuson–Stevens Act. As SCOTUSblog reported in January, the conservation law gives the National Marine Fisheries Service, a federal agency, the power to mandate that “one or more observers” ride on fishers’ boats to collect data “necessary for the conservation and management of the fishery.” In 2020, the agency ruled anglers would be on the hook for the cost too—to the tune of about $700 per day. Herring fishermen sued, and as the cases rose through lower courts, judges invoked Chevron deference, prioritizing the agency’s interpretation of the law and ruling in its favor. Now, in a major victory for industry, the Supreme Court just threw out that precedent.

According to NRDC lawyer David Doniger, who argued the original 1984 Chevron case before the Supreme Court, Chevron deference mattered because Congress can’t possibly weigh in on every last practice of every industry to which a law might apply. That’s what expert agencies are for, he argues, so it makes sense for judges to defer to them. “The only way our government can keep up with the problems that the modern world throws at us is if you have this partnership between Congress and administrative agencies,” he says.

Those who oppose Chevron, however, argue that the doctrine creates constitutional problems and that the interpretation of laws should be left to judges. As lawyer Roman Martinez said in his opening arguments for Relentless, Inc., Chevron “undermines” judges’ duty to interpret federal statutes using their “best and independent” judgment and encourages agency overreach.

In a backward way, the original 1984 case for which Chevron deference was named was actually a win for industry-minded conservatives; the court ruled in favor of the Reagan administration’s EPA, which had re-interpreted an amendment to the Clean Air Act in an effort to limit a pollution regulation. Since then, the late Justice Antonin Scalia and Justice Clarence Thomas have both argued in favor of Chevron. But after President Obama’s time in office, conservatives started souring on the doctrine.

No matter your views on Chevron, there’s no question overturning it will have major implications for how the country’s judicial system operates. Doniger argues that if judges are handed more power to interpret the law, agencies may be more “gun shy” in making policies, partisan groups may judge-shop in selected courts to challenge regulations they oppose, and there may be a general “lack of coherence” in which agency rules are overturned or upheld. In short, he said, it will diminish the government’s ability “to get stuff done.”