A panel of appellate judges on Thursday wrestled with the bounds of the so-called “major questions doctrine” in a challenge to the U.S. Environmental Protection Agency’s fleet-wide tailpipe emissions standards for car makers.

During oral arguments, Chief Judge Sri Srinivasan of the U.S. Court of Appeals for the D.C. Circuit asked attorneys for Republican-led states challenging the Biden administration’s tighter emissions standards if they forfeited their argument that the regulations violate the doctrine by not having raised it in the rulemaking process.