The U.S. Supreme Court Monday questioned whether Michigan has overcharged truckers driving through the state. At issue is a 1991 law passed by Congress that said states could not raise truck registration fees "collected or charged" as of Nov. 15, 1991.

Yellow Freight System argues the state should not be allowed to charge $10 to register its Illinois-plated trucks. If the trucking company prevails, Michigan could have to repay $425,000 and stop charging the fees for any truck with Illinois plates.

States are allowed to charge a registration fee of up to $10 for every truck that passes through its borders. Many states agree to waive fees for trucks that are registered in another state if the other state allows their trucks to pass through without paying a fee, which helps their trucking companies save money.

Michigan previously let trucks with Illinois license plates pass through the state without charging fees. But in September 1991, Michigan changed its policy to say the trucks must have their principal place of business in Illinois - not simply a license plate from the state - to qualify for the waiver.

The Overland Park, KS-based truck firm says its 3,700 trucks with Illinois plates should not have to pay the fees because they weren't required to do so on Nov. 15, 1991.

Michigan Solicitor General Thomas Casey argued the state's fee was $10 at the time. He said the state chose to waive it for some truckers, but has the right to change the policy at any time.

If Michigan wins the case, other states could force trucking companies to pay about $150 million more a year to register their vehicles, Yellow Freight told the court.

The company had won in lower courts, but the Michigan Supreme Court disagreed and allowed the fees. The Supreme Court will decide the case by June 2003.