President Trump is pulling out all the stops to shut down an effort by California to enlist automakers on a plan that would undermine his administration’s effort to roll back strict Obama-era carbon emissions and mileage mandates.

Where it stands: The Justice Department is seeking to determine if Ford, VW, Honda and BMW "violated federal competition law by agreeing with each other to follow tailpipe-emissions standards beyond those proposed by the Trump administration," WSJ reports.

The story cites anonymous sources familiar with the matter. DOJ declined to comment. Ford, Honda and BMW said they will cooperate with DOJ on the matter.

VW couldn't immediately be reached for comment.

On a second front, lawyers for the EPA and the Transportation Department on Thursday warned Mary Nichols, chairwoman of the California Air Resources Board, of legal action if the state tries to set its own rules "that would violate federal law."

Why it matters: The 2-pronged attack stands to escalate tensions between Washington, Sacramento and the auto industry over Trump's plan to freeze emissions standards at 2022 levels, rather than allow them to climb sharply higher.

By targeting the 4 companies that signed the California deal to make cleaner cars, the administration aims to dissuade more automakers from joining.

GM, whose CEO met with Trump on Thursday, is not likely to sign on to the California plan, sources tell Axios.

The Trump administration is cranking up the heat. Multiple reports on Thursday said that the EPA will soon move to revoke California's authority to set its own vehicle pollution rules, Axios' Ben Geman writes.

The bottom line: The administration appears to be taking no chances that California's attempted end run gains momentum while it finalizes its own, looser requirement.