Leading U.S. automakers are making an 11th-hour push to stop the Trump administration from dramatically weakening Obama-era fuel efficiency standards, warning doing so would bring “untenable” uncertainty and lead to drawn-out litigation.

In a letter to President Trump, 17 companies including Ford, General Motors, Toyota, and Volvo, asked him to return to the negotiating table with California, which, with more than a dozen other states, is poised to sue the administration in order to enforce stricter auto pollution rules to limit carbon emissions from transportation, the highest-emitting economic sector. The companies also sent a letter to California Gov. Gavin Newsom, a Democrat, requesting the same thing.

The Trump administration has proposed revoking a Clean Air Act waiver that California has, and more than a dozen other states follow, allowing it to set vehicle emission standards tougher than federal rules.

“Automakers share the environmental idealism of California and the economic pragmatism of the administration in Washington,” Gloria Bergquist, a vice president at the Alliance of Automobile Manufacturers, a trade group representing major automakers, told the Washington Examiner. “Choosing one or the other is neither necessary nor prudent. It’s a false choice. Somewhere between the two is a workable compromise that appropriately balances both of these crucial obligations.

Environmental Protection Agency Administrator Andrew Wheeler previously told the Washington Examiner the Trump administration won’t compromise on its final proposal to be introduced this summer, and will move to revoke the waiver granted to California and other states to set tougher fuel efficiency rules.

The EPA, with the National Highway Traffic Safety Administration, last August proposed freezing Obama-era fuel efficiency rules for cars and light trucks, instead of raising them each year, between model years 2020 and 2026.

The Trump administration argued the tougher Obama rules would make newer cars unaffordable, forcing drivers to use older, less safe, and environmentally unfriendly vehicles.

But the administration and California still sought to reach a compromise before the rule was finalized.

The White House, however, broke off negotiations with California on Feb. 21, and has since tried to convince skeptical automakers to back its plan.

Automakers, who prefer flexibility in the Obama rules, not an outright rejection, consider the Trump plan too extreme. Auto groups have said they hope to maintain a common set of rules with year-over-year increases in efficiency that California would agree to follow, allowing automakers to sell the same models in every state, and avoiding the uncertainty of prolonged litigation.