(CNN) -- Board members of San Francisco's rapid transit system will convene a special meeting next week to discuss the controversial decision this month to cut off cell service in selected stations.
The August 11 move by the Bay Area Rapid Transit System (BART), in an apparent attempt to head off protests against its police officers, drew sharp condemnation from free speech advocates and spurred hackers to launch attacks on the system's website and internal network.
In a letter to passengers sent Saturday and signed by the board's president, Bob Franklin, and interim general manager Sherwood Wakeman, BART defended the decision in claiming it was done "out of an overriding concern for our passengers' safety."
The letter referenced a July 11 protest, in which people railed against the system after several shootings involving its police officers -- the latest coming last month and resulting in the death of 45-year-old Charles Hill.
That spirited and largely peaceful rally at the city's Civic Center stop was organized by a group called "No Justice, No BART," which formed after the 2009 shooting of an unarmed passenger by a BART police officer.
But at the demonstration, video shows one person climbing atop a subway train, before being pulled down. BART also noted in its letter that the protesters blocked doors and generally delayed roughly two-thirds of trains running during the rush-hour commute.
"These actions violated the law by creating a serious threat to the safe operation of the BART system," wrote the agency.
BART police department members learned of another planned protest about a month later, deciding to suspend cell phone service for three hours at select locations in hopes of preventing demonstrators from organizing.
That decision elicited criticism from civil liberty organizations, the San Francisco Chronicle's editorial page and others.
"All over the world people are using mobile devices to organize protests against repressive regimes, and we rightly criticize governments that respond by shutting down cell service, calling their actions anti-democratic and a violation of the rights to free expression and assembly," Rebecca Farmer from the ACLU's northern California office wrote on the advocacy group's website. "Are we really willing to tolerate the same silencing of protest here in the United States?"
Online messages attributed to Anonymous took credit for the apparent hacking last Sunday of myBART.org, a link off BART's website that showed a page featuring, among other items, the hacking group's logo -- a smirking mask above two crossed swords, all on a black background.
In addition, Twitter traffic related to Anonymous boasted that hackers had been able to get into BART's internal network.
"By (cutting cell service), you have not only threatened your citizens' safety, you have also performed an act of censorship," a seemingly computer-generated voice -- speaking over dramatic music and images -- said in a video posted online Sunday afternoon. "By doing this, you have angered Anonymous."
The Federal Communications Commission is collecting information on the matter, with agency spokesman Neil Grace saying Monday by e-mail that "any time communications services are interrupted, we seek to assess the situation."
"We ... will be taking steps to hear from stakeholders about the important issues those actions raised, including protecting public safety and ensuring the availability of communications networks," Grace said.
BART closed, then reopened stations to thwart demonstrators when they gathered again Monday but -- while its officials did not rule out the possibility before -- there was no indication that the suspended cell service again.
In its letter Saturday, BART spoke to First Amendment concerns, stating it recognized people's right to protest "where it can be done safely and without interference with BART's primary mission of providing safe, efficient and reliable public transportation service."
But the letter insisted that suspending cell phone service "did not affect any First Amendment rights of any person to protest in a lawful manner in areas at BART stations that are open for expressive activity. The interruption did prevent the planned coordination of illegal activity on the BART platforms, and the resulting threat to public safety."
The special board meeting to discuss the matter will occur Wednesday, the letter stated.