Representatives Jim Sensenbrenner (R-WI) and Chip Cravaack (R-MN) sent a letter September 10 to the Environmental Protection Agency questioning its authority to set minimum purchase requirements for filling stations selling gasoline containing 15 percent ethanol. The House Republicans charge that the agency overstepped its Clean Air Act authority when it required gasoline retailers selling E15 and E10 from a single dispenser to require customers to purchase at least four gallons as part of their misfueling prevention plans. They asked the agency to respond by September 24.