Maine Sens. Angus King and Susan Collins want the federal Environmental Protection Agency to act on biodiesel production standards.

Biodiesel is a fuel alternative typically made from vegetable oil or animal fat. King, an independent, and Collins, a Republican, are joining a bipartisan group of 30 senators calling for the EPA to set standards. The senators say delays in setting biodiesel production standards are causing plants to reduce production and lay off workers.

The senators say they want the EPA to set production levels under the federal Renewable Fuel Standard program. They cite a study from the National Biodiesel Board that says nearly four-fifths of U.S. biodiesel producers scaled back production in 2014.