Will BART do it again?

That’s the question hanging in the temperate San Francisco air as criticism piles on the Bay Area Rapid Transit system for cutting off cellphone service to some passengers in a bid to thwart an Aug. 11 anti-BART protest being coordinated via mobile devices.

Protesters are set to try again to assemble at a downtown BART station, at the height of Monday’s evening commute , almost daring BART to repeat the service cutoff. On Sunday, the international hacker group Anonymous threatened to shut down BART's website for six hours in retaliation for the transit agency's action.

If anything, BART’s move to preempt the Aug. 11 demonstration has raised the stakes. The original protest was centered on the death of a homeless man, shot by BART police last month during an altercation at a subway station. But Monday’s event has broadened to encompass what BART many critics call censorship, overreach, and tactics akin to those used by Egyptian President Hosni Mubarak as he tried to cling to power amid the Arab Spring uprising.

At the heart of the latest feud is whether the threat to public safety stemming from the protests justifies BART’s cutoff of cellphone service to try to disrupt them. It’s a question vexing authorities concerned about use of social media and services such as BlackBerry Messenger to organize “flash mob” crimes or, as in England last week, violent street riots.

“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,” a BART statement issued Friday said. “BART temporarily interrupted service at select BART stations as one of many tactics to ensure the safety of everyone on the platform.”

So far, the transit agency has few defenders for that decision, at least in public. Besides Anonymous, critics range from a state senator to free-speech experts to a member of BART’s own board.

“We really don't have the right to be this type of censor," Lynette Sweet, who serves on BART's board of directors, told the Associated Press Saturday. "In my opinion, we've let the actions of a few people affect everybody. And that's not fair."

Anonymous, a shadowy group of hackers who retaliate against governments and businesses they deem to impede the free flow of information in cyberspace, now has BART in its sights. "Tomorrow, Sunday – August 14, 2011 at High Noon Pacific Time we, Anonymous – will remove from the internet the web site of BART ... for exactly six hours. That’s twice as long as they shut off the cell phones for," it said in a statement. In the past, Anonmyous has launched denial-of-service attacks on its targets to disrupt operations or business.

BART acknowledged the threat in a statement Sunday. "We’re doing what we can to defend against any attack on the BART website," it said, without calling out Anonymous by name. It assured the public that its website is "wholly separate from any computer network involved in the operation of BART service."

Anonymous has also called for a nonviolent protest at 5 p.m. Monday at the Civic Center BART station in downtown San Francisco.

BART is declining to say if it will again switch off cellphone service at selected underground stations leading up to the event.

"The safety of our customers is our No. 1 priority, and we're going to do what we can to keep people safe," BART spokesman Jim Allision told the San Francisco Chronicle, according to a report early Sunday. "We're just going to leave it at that."

BART has noted that it is illegal to hold rallies or protests on train platforms, which are the ticketed areas of stations for passengers to board and exit trains. A protest last month of the fatal shooting incident did cause service to be interrupted and the Civic Center station to be closed during the rush-hour commute.

Ahead of the Monday protest, BART officials will have occasion to meet with the American Civil Liberties Union’s northern California chapter. The meeting with BART’s police chief was previously scheduled, and the ACLU will add the cell service cutoff to the agenda, spokeswoman Rebecca Farmer told the AP on Saturday.