As the majority pointed out, under the Administrative Procedure Act, “courts must ‘decide all relevant questions of law’” – explicitly including interpreting statutes.

Since 1984, Chevron deference has become pervasive in federal administrative law. By the Supreme Court’s count, 70 of its own decisions in that time have turned on Chevron deference.

More importantly, thousands of lower federal court decisions – more than 400 a year on average – have deployed Chevron deference on issues ranging from Social Security benefits to workplace safety standards, immigration eligibility and environmental protection requirements.

Chevron deference gave many federal agencies broad flexibility to use laws to address new and emerging problems that Congress did not anticipate. But some members of the current Supreme Court – as well as some federal appellate judges – criticized this doctrine, for two key reasons.

First, it authorized executive branch agencies to interpret federal law and forced courts to accept agencies’ reasonable interpretations. However, since the Supreme Court’s 1803 decision in Marbury v. Madison, it has been the duty of courts – not federal agencies – to say what the law is.

Second, Chevron deference arguably allowed federal agencies to grab more regulatory authority than Congress intended them to have, usurping the legislative branch’s responsibility to make law and delegate authority.

The court majority emphasized that prior court decisions upholding agency interpretations based on Chevron deference cannot be challenged solely because of that fact. As Roberts wrote, these holdings “are still subject to statutory stare decisis.”

Stare decisis, or “the thing is decided,” is legalese for why courts will respect prior decisions. In other words, no challenger can go back to a court that relied on Chevron deference and ask the court to change its original decision that the agency’s interpretation was OK.

That’s good so far as it goes. However, many agency interpretations of statutes can be challenged multiple times.

For example, the Clean Water Act protects “waters of the United States.” In 2023, the Biden administration issued new regulations interpreting which bodies of water the law covers. Challengers who disagree with that interpretation can attack the regulations directly and argue that the agencies’ reading of the law is wrong, as the fishing companies did in the Loper Bright cases.

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