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 different protest.
The transit service last Thursday shut down cell phone networks in some stations to stop a protest over a police shooting.
In a city known for civil rights protests and technology, that tactic has landed the commuter train system in a new controversy.
We've invited these protesters now, said Lynette Sweet, a BART director who said managers of the system should not have announced the in-station mobile phone network shutdown.
Anonymous is a loosely knit group that has attacked financial and government Web sites, frequently claiming civil rights motives.
They 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.
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 Web site 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 Peter Henderson)