“The states joining today’s lawsuit represent 140 million people who simply want cleaner and more efficient cars,” California Gov. Jerry Brown said Tuesday. “This phalanx of states will defend the nation’s clean car standards to boost gas mileage and curb toxic air pollution.”

The lawsuit, filed by 17 states and the District of Columbia on Tuesday in a federal appeals court in District of Columbia, accuses the EPA of failing to follow its own regulations and of violating the Clean Air Act. Last month, the Trump Administration said it would revise fuel-efficiency regulations for cars and light trucks, a move supported (and lobbied for) by automakers.

The lawsuit seeks to prevent that rollback.

The Alliance of Automobile Manufacturers, which represents GM, Toyota, Volkswagen, and nine other automakers, sent a letter to EPA head Scott Pruitt calling the fuel efficiency rules “the product of egregious procedural and substantive defects” that are “riddled with indefensible assumptions, inadequate analysis and a failure to engage with contrary evidence.”

The EPA is also considering whether to revoke a waiver that allows California to set its own, more stringent emissions regulations.

The EPA with cooperation from the National Highway Traffic Safety Administration and California Air Resources Board established in 2010 a single national program of greenhouse gas emissions standards for model year 2012-2025 vehicles. The EPA said last year that the standards were appropriate. However, the agency reversed its decision in April and said the standards should be scrapped.

The federal emissions standard is estimated to reduce carbon pollution equivalent to 134 coal power plants burning annually and save drivers $1,650 per vehicle through fuel savings according to the coalition that includes Connecticut, Illinois, Iowa, Minnesota, New Jersey, New York, Pennsylvania, Virginia and Washington.