One of London's busiest Tube stations was open despite a strike by staff in a dispute over the sacking of a colleague.
London Underground said it planned to keep London Bridge open throughout a 24-hour walkout by members of the Rail, Maritime and Transport union, which ends at 10pm.
The union is protesting at the sacking of a member of the station staff, and disciplining of two others over an incident involving an alleged fare dodger.
The RMT maintains the staff should have been praised for tackling a violent passenger.
London Underground disputes the union's version of the incident.
The union is preparing to ballot all its station staff members on LU in an escalation of the row.
RMT general secretary Mick Cash said: "Our members are standing up in support of their victimised colleagues at London Bridge and with LU making it absolutely clear they have no interest in the principles of natural justice we have no option at all but to take this industrial action.
"Despite the spin from LU the facts of this case remain the same.
"It is about a fare dodger stopped and asked to pay his way who then turns violent and attacks staff doing their job.
"LU's message to thugs is that you can keep on fiddling your fares and lay into staff with impunity and it will be the front line Tube workers who get the sack. It is outrageous."
Brian Woodhead, operations director for London Underground, said: "This strike is totally unjustifiable and the version of events given by the RMT union is simply untrue.
"CCTV footage from the station, taken from a number of angles, shows a member of staff displaying unacceptable conduct when dealing with a member of the public.
"The member of staff was dismissed following a thorough investigation.
"The offer to the RMT leadership to view the CCTV footage remains open, and we continue to encourage them to see sense and call off their upcoming ballot asking members across the whole network to strike without knowing the full facts."
Mr Cash said RMT members were "solidly supporting the strike", adding: "The union is well aware that LU have mobilised an expensive and sophisticated scabbing operation that raises serious issues about the safety of the travelling public.
"We will be monitoring that situation throughout the day and filing reports to the regulator."