A BART official, asking not to be quoted by name, said the shutoff was intentionally limited, and someone with an urgent call to make could simply walk up to street level.
But there was disagreement within BART itself. By cutting off demonstrators' ability to send a text message starting a protest, did it violate the rights of bystanders who might be using their cellphones simply to call family or friends?
"I'm just shocked that they didn't think about the implications of this," said Lynette Sweet, who serves on BART's board of directors. "We really don't have the right to be this type of censor. In my opinion, we've let the actions of a few people affect everybody. And that's not fair."
ABC station KGO-TV contributed to this story. Additional information from The Associated Press.