The Trump administration formally rolled back California's authority to set automotive vehicle emission standards, a move state officials have vowed to fight in the courts. At a press conference on Thursday, Environmental Protection Agency Administrator Andrew Wheeler and Transportation Secretary Elaine Chao announced that the EPA would withdraw the 2013 Clean Air Act waiver that enabled California to set its own tailpipe greenhouse gas emission standards.

President Trump touted the move by tweet on Wednesday, saying that it would result in less expensive and safer cars, and insisting that new cars would be cleaner, even though they will burn more gasoline than they would have under the fuel efficiency standards established during President Obama's administration.

The rollback is a part of the new National Highway Traffic Safety Administration (NHTSA) and the EPA "One National Program Rule," which, as the name states, means the federal government will have one set of nationwide fuel economy and greenhouse gas emission standards for automobiles and light-duty trucks.

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"No state has the authority to opt out of the nation's rule, and no state has the right to impose its policies on everybody else and our whole country," Chao said Thursday.

Wheeler told reporters that having one standard will provide stronger "regulatory certainty" for the automotive industry. The Automobile Alliance said in a statement that "we support one national program as the best path to preserve good auto jobs, keep new vehicles affordable for more Americans and avoid a marketplace with different standards."

However, in July, four automakers — Ford, Honda, BMW and Volkswagen — had agreed to meet Califronia's stricter tailpipe emissions, rather than the federal standard. Some of the automakers believe that without a substantial increase in fuel efficiency, their vehicles could be less competitive in the global marketplace, since several other nations demand higher fuel economy than the U.S. The Trump administration has opened an antitrust investigation into the deal between the automakers and California.

The president also seeks to relax Obama-era federal mileage standards nationwide, weakening a key effort by his Democratic predecessor to slow climate change. The Trump administration's original proposal would have frozen the Obama EPA's increase in standards at about 37 miles per gallon in 2021. President Obama issued a rule that demanded that fuel economy grow every year through 2026, when it would reach a 46.7 mile-per-gallon average for a company's fleet.