7:36 Police began arresting protesters who were blocking Market street, a little earlier.
7:17 Civic Center and Powell Stations are closed. Protesters are still gathered on Market.
6:41 Civic Center Street Station is closed again. BART reports that Powell Street is open.
6:37 Powell Street Station is closed again.
6:19 p.m. All BART and Muni Stations are open.
6:11 p.m. Some entrances are opened at Powell Street Station.
5:51 p.m. Powell Street Station closed to BART and Muni.
5:35 p.m. Dornhelm reports that there are about 15 to 20 protesters at the station, with about 20 police facing them.
5:29 p.m. Trains are beginning to go through, Civic Center Station is closed. BART declares illegal assembly.
5:20 p.m. At the beginning of the protest three people were arrested for interfering with the operation of a railroad.
5 p.m. There seemed to be a rush of passengers just before 5 p.m. at Civic Center Station, reports KQED's Rachel Dornhelm.
BART police and SFPD also have a presence at the station. About 100 BART officers are managing the protest this afternoon, BART police said.
Commuters, protesters and BART employees are all gearing up for another protest organized by Anonymous.
On July 3 BART police officers shot and killed Charles Hill at Civic Center Station. On July 11, in a protest over that shooting, some demonstrators held open train doors, stopped BART trains from continuing, and one protester climbed on top of a train.
BART has been criticized for shutting down cellphone service during the protest.
Anonymous, a loose collective of activists and "hacktivists" then called for a protest last week, lashing out at what they, and the ACLU, see as an affront to their right to freedom of speech. During that rally, protesters managed to shut down all four downtown BART stations. Anonymous is calling for protesters to march again today at 5pm.
This time BART is warning stations may be closed again, if necessary to protect passenger safety, spokesman Jim Allison told Dornhelm.
Last week, BART rider Steve Solnit was stuck at Embarcadero Station after it was closed.
"When BART goes out of service they have something called a bus bridge where local transit agencies provide buses to BART station to BART station. They didn't even have that ready," Solnit said. "To me its a complete failure of BART management."
BART will not have shuttles this time either, Allison said.
"Unlike Chicago transit or others, we don't have buses at our disposal," Allison said. "We have trains to get people home."
BART is in contact with SFPD and the city's Sheriff Department over tonight's planned protest as well, he said. The cost of the policing, and protests, comes out of BART's general fund.