Transit officials said Friday they blocked cell phone reception in San Francisco stations for three hours to disrupt a planned demonstrations over a police shooting.

Officials with the Bay Area Rapid Transit system, better known as BART, said they turned off the electricity to cell phone towers in four stations from 4 p.m. to 7 p.m. Thursday. The move was made after BART learned that protesters planned to use mobile devices to coordinate a demonstration on train platforms.

"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," BART officials said in a prepared statement.

The statement noted that it's illegal to demonstrate on the platform or aboard the trains. BART said it has set aside special areas for demonstrations.

The American Civil Liberties Union questioned the tactic.

"Shutting down access to mobile phones is the wrong response to political protests," the ACLU's Rebecca Farmer said in a blog post.

BART officials were confident the cell phone disruptions were legal. The demonstration planned Thursday failed to develop.

"We had a commute that was safe and without disruption," said BART spokesman Jim Allison.

The demonstrators were protesting the July 3 shooting of Charles Blair Hill by BART police who claimed Hill came at them with a knife.

A July 11 demonstration disrupted service during the rush-hour commute, prompting the closing of BART's Civic Center station. Several arrests were made.