U.S. immigration officials have begun preparing for a major sweep in San Francisco and other Northern California cities in which federal officers would look to arrest more than 1,500 undocumented people while sending a message that immigration policy will be enforced in the sanctuary state, according to a source familiar with the operation.

Officials at Immigration and Customs Enforcement, known as ICE, declined to comment Tuesday on plans for the operation.

The campaign, centered in the Bay Area, could happen within weeks, and is expected to become the biggest enforcement action of its kind under President Trump, said the source, who requested anonymity because the plans have not been made public.

Trump has expressed frustration that sanctuary laws — which seek to protect immigrants and persuade them not to live in the shadows by restricting cooperation between local and federal authorities — get in the way of his goal of tightening immigration.

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