BART's actions are a violation of established U.S. law, "plain and simple," Siy said. The Communications Act says telephone carriers and their agents cannot "discontinue, reduce, or impair service to a community, or part of a community" without FCC approval.

In addition, California's Second District Court of Appeal, in 1942 case People v. Brophy, ruled that no state official has the authority to suspend phone service on the "mere assertion that illegal activity might take place," the petition said.

BART has defended its actions, saying it cut service to ensure safety. "Organizers planning to disrupt BART service on August 11, 2011 stated they would use mobile devices to coordinate their disruptive activities and communicate about the location and number of BART Police," BART said in a statement posted to its website. "A civil disturbance during commute times at busy downtown San Francisco stations could lead to platform overcrowding and unsafe conditions for BART customers, employees and demonstrators."

Protestors had planned to chain themselves onto BART subway cars, potentially trapping more than 8,000 passengers in a 3.4-mile tunnel at the bottom of the San Francisco Bay, said Bob Franklin, president of BART's board of directors. An emergency situation in a trapped train would have been difficult to respond to, he said.

"The intent was to protect passenger safety, not to stop a protest," he added.