The Trump administration has announced plans to freeze auto mileage and pollution standards, picking a fight with California.

The Transportation Department and Environmental Protection Agency jointly proposed Thursday that automakers not be required to keep making vehicles more efficient and less polluting beyond the 2021 model year.

That means automakers would only have to achieve an average of 37 mpg, not the 50 mpg goal envisioned by the Obama administration. Standards on greenhouse gas emissions would also be relaxed.

The Trump administration justified the rollback on safety grounds, arguing that more efficient vehicles would cost more, prompting drivers to keep them longer, resulting in a higher share of older, less-safe cars on the road. Forbes magazine called the argument “creative math.”

California officials immediately criticized the plan, noting that the Golden State has consistently led the nation in establishing clean air and energy goals.

“This regulatory rollback by the Trump Administration completely disregards Americans’ health and undermines our work to keep our air and water clean,” said Rep. Scott Peters, who represents the 52nd District in San Diego County. “It also stifles innovation and competition that has created more efficient, cleaner engines that can power our future.”

The Trump plan would also revoke states’ rights to set their own pollution standards, and California Gov. Jerry Brown vowed that California would fight back, enlisting 18 other states in suing the federal government to prevent what he called a “reckless scheme.”

“Motorists will pay more at the pump, get worse gas mileage and breathe dirtier air,” Brown said. “California will fight this stupidity in every conceivable way possible.”