A federal court already has temporarily blocked the three waivers Trump’s EPA granted to small refineries, excusing them from the requirement to blend ethanol into gasoline. Grassley said the waivers are part of a flawed system. “One of the problems we’ve had with how that program’s administered is there’s not enough transparency in it,” Grassley said.

Due to the way the EPA has run the program, it’s still not clear which refineries were granted these last-minute waivers. Republican Joni Ernst, Iowa’s other U.S. Senator, has not commented on the last-minute Trump Administration waivers from ethanol blending requirements.