A federal grand jury is investigating whether San Francisco's policy of offering sanctuary to undocumented immigrants violates U.S. laws against harboring people who are in the country illegally, city officials say.

City Attorney Dennis Herrera said his office has hired a criminal defense lawyer to represent employees who might be questioned or asked for documents. He and Mayor Gavin Newsom said they would cooperate with the investigation...

Herrera's office was notified of the investigation several weeks ago when the grand jury issued a subpoena for documents. It's not clear whether prosecutors are seeking evidence of possible criminal violations by city officials...