The mayor of a sanctuary city in California issued a warning that U.S. Immigration and Customs Enforcement (ICE) could be conducting a raid in the area as soon as Sunday — ratcheting up tension with the feds while giving her constituents an early heads-up.

Libby Schaaf, the Democratic mayor of Oakland, shared the warning — which she said she “learned from multiple credible sources” — in a press release on Saturday, “not to panic our residents but to protect them,” Fox 2 reported.

The mayor said she didn’t know further details of the ICE operation, but claimed she felt it was her “duty and moral obligation as Mayor to give those families fair warning when that threat appears imminent.”

The feds detained at least four people Sunday, a program manager for the San Francisco Immigrant Legal Education Network told the San Francisco Examiner, although the paper noted it was unclear if the detentions were related to any broader ICE operation.

Schaaf during a news conference on Sunday also said she told mayors of other Bay Area cities of the impending ICE sweep, SFGate reported.

Her tweet on Saturday aligned with previous reports that law enforcement officials in Northern California would not cooperate with ICE, and noted state law “prohibits business owners from assisting ICE agents in immigration enforcement and bars federal agents from accessing employee-only areas.”

Schaaf, who is seeking reelection, said in January that she’d be willing to go to jail to defend the city’s sanctuary city status, and has openly opposed the Trump administration’s crackdown on illegal immigration.

“It is no surprise that the bully in chief is continuing to try to intimidate our most vulnerable residents,” Schaaf said at the time. “We're very clear that our values are to protect all of our residents regardless of where we come from. We want to protect families, not tear them apart.”

WHAT ARE SANCTUARY CITIES?

And California Lt. Gov. Gavin Newsom, who’s running for governor, commended Schaaf’s public warning, telling SFGate: “We can and must protect immigrant families from Donald Trump’s mass deportations. I want to thank Mayor Schaaf for her courage and hope more local leaders will follow her lead.”

ICE told KGO-TV on Saturday that the bureau was unsure what Schaaf was referring to as “There are ICE operations every day.”