The hacker group Anonymous is taking on San Francisco’s subway system after the Bay Area Rapid Transit turned off cell phone service in stations last week to foil a protest over a police shooting.

Anonymous, a loosely knit group that has attacked financial and government websites, has called for protesters to descend on the Civic Center station in San Francisco at 5 p.m. on Monday, publicizing the action with tweets from @YourAnonNews.

The transit service shut down cell phone networks in some stations on Thursday to stop demonstrators from organizing a protest over the fatal shooting of a man by police last month.

Lynette Sweet, a BART director, said managers of the system should not have announced the phone network shutdown. In a city known for civil rights protests and technology, that tactic has landed the commuter train system in a new controversy.

Would-be protesters were encouraged to download software for short-range mobile-to-mobile messaging, in case the in-station networks are shut down again.

BART said that a website for its users, myBART.org, had been hacked over the weekend, and that contact information from at least 2,400 people had been stolen.

(Reporting by Emmett Berg, editing by Anthony Boadle)