A war between the Trump Administration and the state of California has been , with the former trying to relax vehicle emissions regulations and the latter refusing to relinquish its own power. Now things may be coming to a head, with reporting that the White House will formally revoke California’s legal right to set its own tailpipe emissions rules sometime on Wednesday.

California’s Air Resources Board currently sets the state’s vehicle emissions standards—the strictest ones in the U.S. This can be traced back to the 1970 Clean Air Act, which granted California a waiver to set stricter rules of its own since it already had rules in place before the federal law happened.

In addition to being America’s largest new car market, California also sets emissions regulations for 13 other states that follow its lead.

But the Trump Administration has for a long time voiced its desire to roll back emissions standards in an effort to allegedly reduce new vehicle costs—, according to a number of news outlets.

Doing so would require the revocation of the aforementioned waiver. The Times writes that, at some point tomorrow, the Trump administration is going to try to strip California of its right to set these standards, thereby making the EPA’s standards the one that all 50 states must abide by.

From the Times:

The formal revocation of California’s authority to set its own rules on tailpipe pollution — the United States’ largest source of greenhouse emissions — will be announced Wednesday afternoon at a private event at the Washington headquarters of the Environmental Protection Agency, according to two people familiar with the matter.

California’s response? Exactly what you’d expect. They’re not having it. From the article:

Xavier Becerra, the attorney general of California, wrote in an email: “California will continue its advance toward a cleaner future. We’re prepared to defend the standards that make that promise a reality.”

According to the story, the administration has been having a set by the Obama administration, thanks in part to the EPA allegedly struggling to justify the move with data, California refusing the decision, and automakers negotiating an agreement with California.

That last bit, which occurred earlier this summer when automakers agreed with California on strict (but not quite as strict as initially proposed) standards, made the Commander-In-Chief a bit upset, as shown in these tweets:

But as much trouble as the White House has had in rolling back standards, it’s the removing of California’s authority to set its own that seems to be the priority, with the Times writing:

As a result, the White House decided to proceed with just one piece of its overall plan — the move to strip California of its legal authority to set tougher standards — while delaying the release of its broader rollback, according to these people.

You can be sure that California will fight this. And the White House is apparently counting on it, which is why timing is so critical, as the Times writes:

White House officials have also been eager to move quickly to revoke California’s authority to set its own standards because they want the opportunity to defend the legal effort to undo emissions regulations in the Supreme Court before the end of Mr. Trump’s first term. The thinking goes that if a Democrat were to be elected president in 2020, the federal government would be unlikely to defend revocation of the waiver in the high court.

You can expect to hear more on this tomorrow.