Thousands of commuters were delayed Thursday as one of the busiest lines on the London subway system was closed in a dispute over safety.
Management suspended service on the Northern Line late Wednesday after drivers expressed fears about problems with the trains' emergency brakes.
Unions representing the drivers said they would support any members who refused to operate the trains.
London Underground said it was holding talks with unions in an attempt to resolve the dispute. It said the Northern Line, which carries more than 600,000 passengers a day, would be closed until further notice, reports the AP.