California filed a lawsuit October 2, 2026 as part of a coalition of 26 states and local governments challenging the Trump administration’s final rule weakening corporate average fuel economy (CAFE) standards for new passenger cars and light trucks.
The coalition argues that NHTSA adopted standards less stringent than the “maximum feasible level” Congress requires under federal law. Attorney General Rob Bonta’s office said stronger fuel economy requirements have helped motorists save money by reducing the amount of fuel their vehicles use. The coalition brought the challenge in the U.S. Court of Appeals for the First Circuit.
NHTSA’s final rule lowers the projected fleetwide fuel economy average for model year 2031 to 34.9 miles per gallon, compared with 50.4 mpg under the Biden administration’s standards, according to news reports.
The U.S. Department of Transportation released the rule on September 28, 2026. The administration said in its release that the Biden administration standards went “far beyond the requirements mandated by Congress” and “created a backdoor electric vehicle mandate.”
Coalition challenges agency analysis
In its lawsuit, the coalition alleges that NHTSA violated the Energy Policy and Conservation Act and the Administrative Procedure Act by failing to establish the maximum feasible fuel economy standards. It argues that the agency improperly excluded existing electric vehicles from its baseline analysis and adopted requirements below the efficiency the fleet achieved in 2021.
Bonta’s office also challenges the agency’s treatment of fuel savings, vehicle affordability, safety, and climate damages. It says the rollback would eliminate nearly $220 billion in fuel savings available under the previous standards. The rule also ends CAFE credit trading in 2028, which the state says would harm California’s electric vehicle industry.
Administration cites vehicle affordability
The Trump administration defended the rollback as a way to lower vehicle prices and reverse standards the administration considers an indirect electric vehicle mandate.
The administration’s analysis estimates that model year 2031 vehicles would cost an average of $1,289 less under the revised rule. Drivers would, however, incur more than $1,600 in additional fuel costs over the life of the vehicles, compared to the previous standards. The U.S. Department of Transportation said the rule would increase US gasoline consumption by 4.6% through 2050, compared to the prior standard, and would increase new car sales, according to news reports.