On Thursday, the administration proposed freezing vehicle fuel economy requirements at the 2020 level and revoking California’s authority under the Clean Air Act to set more stringent tailpipe emissions rules in the state.

But California, a state that has long prioritized lowering its emissions—even going so far as beating its 2020 emissions target four years early, will not take these changes lying down. California governor Jerry Brown vowed Thursday to “fight this stupidity in every conceivable way possible.”

“For Trump to now destroy a law first enacted at the request of Ronald Reagan five decades ago is a betrayal and an assault on the health of Americans everywhere,” Brown said. “Under his reckless scheme, motorists will pay more at the pump, get worse gas mileage, and breathe dirtier air.”

California has previously sued the Trump administration over its auto policies, and the state announced plans for a new lawsuit following Thursday’s announcement. California attorney general Xavier Becerra announced that he would lead 19 attorneys general in a new lawsuit, saying that “California is about progress and 21st century innovation and technology. We’re not about backsliding.”

“The earth is not flat and climate change is real. Can someone please inform the folks at the White House?” he added.

A number of California lawmakers demonstrated their own intention to combat the administration’s proposal, with Senators Kamala Harris and Dianne Feinstein introducing a resolution in the Senate that would allow California to remain autonomous in its clean air policies. A similar measure was also introduced in the House.

Former California governor Arnold Schwarzenegger, a Republican, also condemned the administration’s policy, noting that it was Reagan who had first requested California’s waiver. On Thursday, he tweeted that “this is a stupid policy and no one asked for this,” adding that “if the president thinks he can win this fight, he’s out of his mind.”