Last year, the Trump administration threatened to revoke California’s waiver which allows the state to impose stricter fuel economy and emission standards than the federal government.

At the time, then EPA administrator Scott Pruitt said “Cooperative federalism doesn’t mean that one state can dictate standards for the rest of the country.” The agency also warned “The California waiver is still being reexamined by EPA under Administrator Pruitt’s leadership.”

Fast forward to today and it appears the Trump administration is preparing to follow through with its threat. According to sources who talked to Reuters, the EPA and National Highway Traffic Safety Administration are preparing to submit a “plan to revoke California’s authority to set its own vehicle greenhouse gas standards and declare that states are pre-empted from setting their own vehicle rules.”

Also Read: EPA Withdraws 50 MPG Target By 2025, Threatens California

The details are plan remain unclear, but would reportedly gut California’s ability to influence emission standards for a vast majority of vehicles including those with zero-emission powertrains. However, the publication says it wouldn’t have any effect on their ability to set standards for low-emission vehicles.

The plan is reportedly being called the “One National Program rule” and it echoes Pruitt’s argument that it is in “America’s best interest to have a national standard” for fuel economy and emissions.

The battle between California and the Trump administration has been brewing ever since the EPA decided an Obama-era proposal to require vehicle fleets average 46.7 mpg by 2025 was “wrong” and “should be revised.”

Over a dozen states quickly filed suit claiming the EPA acted “arbitrarily and capriciously,” violated the Clean Air Act and failed to follow its own rules and regulations. The issue came to a head more recently when four automakers – BMW, Ford, Honda and Volkswagen – agreed to follow rules implemented by the state of California.

That sparked the ire of President Trump who tweeted “Henry Ford would be very disappointed if he saw his modern-day descendants wanting to build a much more expensive car, that is far less safe and doesn’t work as well, because execs don’t want to fight California regulators.” The President went on to claim California will “squeeze them to a point of business ruin.”