A group of car manufacturers have co-signed a letter to President Donald Trump asking him to reconsider the planned rollback of emissions standards in the United States or risk threatening significant cuts to their profits.

According to The New York Times, the letter is signed by 17 companies, including the likes of Ford, GM, Volvo, Toyota, BMW, and Volkswagen.

In it, the automakers express serious concerns about how Trump’s drastic regulation change could split the auto market in two, as California and 13 other states are expected to continue enforcing their own, stricter norms.

“We strongly believe the best path to preserve good auto jobs and keep new vehicles affordable for more Americans is a final rule supported by all parties — including California,” the letter reads.

Also Read: Automaker Lobby Asks Trump To Roll Back Obama’s Strict CAFE Rules

Many car manufacturers rallied behind Trump early on during his presidency, encouraging him to roll back emissions standards set in place by the Obama administration. They now believe the President is going too far and want to find a middle ground between what the former and the current federal proposals.

Trump’s revised regulation would essentially eliminate Obama’s pollution rules, virtually freezing mileage standards at about 37 mpg for cars, compared to the previous target of 54.5 mpg by 2025.

If the Trump administration follows through with its proposal, California and 13 other states are tipped to sue and continue enforcing their current rules.

“Our thinking is, the rule is still being finalized, there is still time to develop a final rule that is good for consumers, policymakers and automakers,” vice president of the Alliance of Automobile Manufacturers, Gloria Bergquist said.

There are reportedly fears within the industry that criticizing Trump’s plans presents a number of risks, with some believing the President may retaliate with new tariffs on auto imports.