The U.S. Supreme Court agreed to decide whether railroads and their employees must pay millions of dollars in taxes when workers exercise stock options.

The justices said they’ll hear an appeal by U.S. units of Canadian National Railway Co. that are seeking $13 million in refunds from the federal government.

The issue is whether some types of stock workers receive through options qualify as taxable compensation under a federal law that applies to the railroad industry. The law imposes taxes on the industry to pay for retirement benefits.

The Trump administration joined the railroad industry in urging the court to hear the case, pointing to disagreement among federal appeals courts. The administration said almost $100 million is at stake in pending and recently decided cases alone.

The administration says the appeals court in the Canadian National case correctly concluded that the stock is taxable.

The case is Wisconsin Central v. United States, 17-530.