The justices are weighing appeals by two fishing companies of lower court rulings allowing the National Marine Fisheries Service to require commercial fishermen to help fund the program. The companies - led by New Jersey-based Loper Bright Enterprises and Rhode Island-based Relentless Inc - have argued that Congress did not authorize the agency, part of the U.S. Commerce Department, to establish the program.

More broadly, the companies have asked the court, with its 6-3 conservative majority, to rein in or overturn a precedent established in 1984 that calls for judges to defer to federal agency interpretation of U.S. laws deemed to be ambiguous, a doctrine called "Chevron deference."

The bid by the commercial fishermen, supported by various conservative and corporate interest groups including billionaire Charles Koch's network, is part of what has been termed the "war on the administrative state," an effort to weaken the federal agency bureaucracy that interprets laws, crafts federal rules and implements executive action.

The Supreme Court has signaled skepticism toward expansive regulatory power, issuing rulings in recent years to rein in what its conservative justices have viewed as overreach by the Environmental Protection Agency and other agencies.

The fish conservative program was started in 2020 under Republican former President Donald Trump. It is being defended by Democratic President Joe Biden's administration. The regulation at issue called for certain fishermen to carry aboard their vessels U.S. government contractors and pay for their at-sea services while they monitored the catch.

The program aimed to monitor 50 percent of declared herring fishing trips in the regulated area, with program costs split between the federal government and the fishing industry. The monitors assess the amount and type of catch including species inadvertently caught.

The cost of paying for the monitoring was an estimated $710 per day for 19 days a year, which could reduce a vessel's income by up to 20 percent, according to government figures.

The Biden administration has said the program is authorized under a 1976 federal law called the Magnuson-Stevens Act to protect against overfishing in U.S. coastal waters. It said in court papers the program was suspended for the fishing year starting in April 2023 due to insufficient federal funding.

The Washington-based U.S. Court of Appeals for the District of Columbia Circuit and the Boston-based 1st U.S. Circuit Court of Appeals both ruled in favor of the government.

Other cases now before the Supreme Court also involve the scope of agency powers.

During arguments in November, the conservative justices signaled skepticism toward the legality of certain proceedings conducted in-house by the Securities and Exchange Commission to enforce investor-protection laws. During arguments in October, the court appeared skeptical of the payday lending industry's challenge to the Consumer Financial Protection Bureau's funding structure.

Rulings in the fishing, SEC and CFPB cases are expected by the end of June.

(Reporting by John Kruzel; Editing by Will Dunham)

By John Kruzel and Andrew Chung