Federal officials said Tuesday they arrested more than 150 undocumented immigrants in a Northern California sweep aimed at countering local sanctuary laws, while suggesting Oakland Mayor Libby Schaaf’s decision to alert the public to the secret operation may have allowed some targets to elude capture.

Since Sunday, U.S. Immigration and Customs Enforcement officers have fanned out from the Central Valley to the far northern reaches of the state, knocking on doors, detaining people and prompting alarm from community activists and some Democratic politicians who oppose President Trump’s immigration crackdown.