U.S. Transportation Secretary Sean Duffy warned Sunday that he’s about to make good on a threat to revoke millions in federal funds for California because he says the state is illegally issuing commercial driver’s licenses to noncitizens.

In an appearance on Fox News Channel’s “Sunday Morning Futures” Duffy said California Gov. Gavin Newsom has refused to comply with U.S. Department of Transportation rules that require the state to stop issuing such licenses and review those already issued.

“So, one, I’m about to pull $160 million from California,” Duffy said. “And, as we pull more money, we also have the option of pulling California’s ability to issue commercial driver’s licenses.”

Newsom’s press office did not respond to an email seeking comment on the matter Sunday, but California has defended its practices previously. When Duffy threatened to revoke funds last month, a spokesperson for Newsom dismissed the attack and noted that CDL holders from California have a significantly lower rate of crashes than both the national average and the Texas average, which is the only state with more licensed commercial drivers.

Last month, the Transportation Department tightened commercial driver’s license requirements for noncitizens after three fatal crashes that officials said were caused by immigrant truck drivers.