The Supreme Court ruled Friday that judges have been giving too much deference to unelected bureaucrats and must reclaim some of that decision-making — a decision that could slow the expansion of the administrative state.

The justices, in a 6-3 ruling, overturned a 1980s-era ruling known as the Chevron case that said when the laws written by Congress were ambiguous, judges should try to defer to the experts in the executive branch for their interpretation.

Chief Justice John G. Roberts Jr. overturned Chevron, saying it’s time judges started judging.

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“Courts must exercise their independent judgment in deciding whether an agency has acted within its statutory authority, as the [Administrative Procedure Act] requires,” he wrote, joined by the court’s other five GOP-appointed members. “Careful attention to the judgment of the Executive Branch may help inform that inquiry. And when a particular statute delegates authority to an agency consistent with constitutional limits, courts must respect the delegation, while ensuring that the agency acts within it. But courts need not and under the APA may not defer to an agency interpretation of the law simply because a statute is ambiguous.”

He said the ruling does not, however, call into question the massive amount of cases decided over the last four decades using Chevron.

That could head off a wave of litigation asking the courts to re-decide thousands of agency actions over the last 40 years.

The court’s three Democratic appointees dissented, calling the ruling the latest move in an ongoing campaign by conservative legal minds “to roll back agency authority.”

Justice Elena Kagan said Chevron has become the bedrock of modern American government, allowing experts at federal agencies to control key decisions.

“Agencies have expertise in those areas; courts do not,” she wrote.

She said Congress has willingly turned these sorts of complex decisions over to the agencies, and the courts should not upend that.

But Chief Justice Roberts said Chevron deference and the legal tests judges have invented to apply it, have become “unworkable.”

Indeed, the Supreme Court had already tossed Chevron on the ash heap and hadn’t used it to uphold an agency’s action in nearly a decade. But lower courts were still bound by it — until now.

“Today, the Court places a tombstone on Chevron no one can miss,” wrote Justice Neil M. Gorsuch, who was part of the majority.

The decision was met with loud cheers from Republicans and anger from Democrats, who said the Supreme Court had gone “out of control.”

“Today’s decision provides yet more proof that the far-right supermajority on the Supreme Court will cast aside whatever precedent it wants in its quest to increase its own power and that of its MAGA allies across the country,” said Rep. Jerrold Nadler, the top Democrat on the House Judiciary Committee, and Rep. Lou Correa, top Democrat on the administrative state subcommittee.

The legal battle was brought by fishermen challenging a federal rule that had them footing the bill for federal agencies to monitor their catch.

It challenged what is known as “Chevron deference” — a term of art lawyers gave to how courts have treated the 1984 ruling, which involved a fight between the energy giant and the Environmental Protection Agency and its environmental allies.

That court, in a 6-3 ruling in Chevron U. S. A. Inc. v. Natural Resources Defense Council Inc., said the EPA’s interpretation of a law was reasonable and that courts should defer to agency judgment in cases in which the law was ambiguous.

The fishermen were able to upset that decision in their case on Friday.

They argued the National Marine Fisheries Service has run amok with a plan to charge fishing vessels as much as $700 a day to hire a monitor to police their catch. The fishers lost in the federal appeals courts and brought the legal battle to the high court.

To defenders, Chevron blazed a path to good government, putting the experts at federal agencies in charge of the finer points of policymaking.

To detractors, Chevron is the stuff of Orwellian dystopias, siphoning massive amounts of political power away from Congress and the courts and turning it over to unelected and usually anonymous bureaucrats.

In the ensuing decades, the case has become legendary, less for what it said than the way it has been used by some lower courts — particularly the appeals court in Washington that handles many agency cases — to create a presumption in favor of an agency’s decisions.