Conservative Supreme Court justices on Wednesday voiced support for weakening the power of federal regulators, but it was not clear whether a majority would overturn a precedent that has guided American law for four decades over everything from the safety of food and drugs to environmental protection.

Billions of dollars are potentially at stake in front of a court that, like the rest of the federal judiciary, was remade during Donald Trump’s presidency by conservative interests that were motivated as much by weakening the regulatory state as social issues including abortion.

The court heard three and a half hours of arguments in two challenges brought by commercial fishermen to a fee requirement, though the facts of their cases were barely discussed in the courtroom. Instead, the focus was on whether the court should overturn the 1984 case colloquially known as Chevron, a decision that has been the basis for upholding a wide range of regulations public health, workplace safety and consumer protections.

Lower courts used the Chevron decision to uphold a 2020 National Marine Fisheries Service rule that herring fishermen pay for government-mandated observers who track their fish intake.

Two of Trump’s appointees, Justices Neil Gorsuch and Brett Kavanaugh led the attack on the Chevron decision, which says that when laws aren’t crystal clear, federal agencies, and the experts that serve in them, should be allowed to fill in the details as long as they come up with a reasonable interpretation.

Gorsuch noted that some judges invoke the Chevron doctrine frequently and others, not at all. “Shouldn’t that be a clue that something needs to be fixed here?” Gorsuch asked Solicitor General Elizabeth Prelogar, defending the decision on behalf of the Biden administration.

When Prelogar talked about the shock to the legal system that would result from overturning such a longstanding and far-reaching precedent, Kavanaugh suggested that Chevron is to blame for the regulatory flip-flops that happen when a president of one party replaces a president of the other.