The Trump administration is revoking California’s waiver on automotive emissions, which could also affect requirements for marine engines.

President Trump announced the move on Twitter, according to USA Today, saying the revocation would save consumers money “while at the same time making the cars substantially SAFER.” He said the cars would cost less, encouraging drivers to buy newer models.

Officials with the Environmental Protection Agency and the Department of Transportation are supposed to announce the details of the decision in a news conference today.

EPA officials reportedly sent officials in California a letter last week, warning that tougher emissions rules violate federal law. Other states have allegedly considered adopting the California standard and four auto manufacturers signed an agreement this summer supporting the lower emission requirements, which drew Trump’s ire on Twitter.

Revoking the waiver would affect 13 states considering enacting their own standards: Connecticut, Delaware, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont and Washington.

California officials used the waiver earlier this summer to reach deals with Ford, Volkswagen, BMW and Honda.

In a statement, California Attorney General Xavier Becerra said, “If the administration intends to argue that public health and safety will be improved by overturning the waiver, we’ll enjoy facing them in court.”