For decades, the Clean Air Act has authorized the Environmental Protection Agency (EPA) to issue motor vehicle emissions standards that reduce harmful pollution by encouraging or requiring the development of cleaner technologies. In 2024, the EPA issued new standards for heavy-duty vehicles, limiting the greenhouse gases and pollutants that vehicles can emit. These standards took into account recent technological advancements, including the increased viability of electric vehicles as an emissions-reduction tool. A group of states and fuel-industry participants challenged the new standards in the U.S. Court of Appeals for the D.C. Circuit, relying heavily on the “major questions doctrine” and arguing that the standards exceed the EPA’s authority. In January 2025, CAC filed an amicus brief in support of the EPA. Our brief makes three main points. 

First, we explain that under Supreme Court precedent, the major questions doctrine applies only in “extraordinary” cases, where an agency’s assertion of breathtaking new power reflects a dubious effort to transform the fundamental nature of its authority. Supreme Court decisions have consistently demonstrated that more is needed to implicate the doctrine than economic and political significance alone; other factors must indicate that the agency is subverting congressional intent by seeking “an unheralded power representing a transformative expansion in its regulatory authority.” 

Second, we show that the requirements for applying the major questions doctrine are not satisfied in this case. Although the challengers claim that the EPA is exceeding its mandate by forcing too big a shift toward electrification, there is nothing novel or unprecedented in the agency’s new standards. Accounting for technological improvements like electrification in determining the feasibility of emissions reductions does not transform the authority Congress conferred on the EPA. Instead, the agency is fulfilling the Clean Air Act’s statutory command as it always has: using its expertise to balance public health, technological advancements, and costs to manufacturers and consumers. 

Third, we argue that extending the major questions doctrine to cases like this would undermine traditional statutory interpretation and constitutional principles. We discuss how the major questions doctrine is in tension with textualism because it emphasizes pragmatic considerations outside the statutory text. The Supreme Court’s recent Loper Bright decision underscores that all statutes “have a single, best meaning,” and that ambiguity does not relieve courts “of their obligation to independently interpret” statutes using “the traditional interpretive tools.” A court may not short-circuit its inquiry into a statute’s best meaning simply because significant issues are at stake. We also explain that overuse of the major questions doctrine would undermine the separation of powers and thrust the courts beyond their proper role in interpreting the law. A presumption that Congress would not leave major decisions to agencies runs contrary to congressional practice dating to the Founding. If the judiciary starts to reject agency initiatives on the ground that their practical effects are too broad, it risks eroding the courts’ status as non-political arbiters of the law. 

The D.C. Circuit should therefore decline to apply the major questions doctrine and should uphold the EPA’s standards.