Justice Amy Coney Barrett on Friday wrote her first dissent in a case involving exemptions given to smaller oil refineries from a federal law that requires increased amounts of ethanol and renewable fuels to be blended into their gas.

The court’s majority, led by Justice Neil Gorsuch, found that a lower court had erred in ruling against the Environmental Protection Agency. The case arose after the EPA gave two smaller gas companies, HollyFrontier and CVR Energy, an extended exemption from the renewable fuel standard requirements of the Clean Air Act, even after their original exemptions had expired. The decision is a major setback for biofuel companies.