London bus workers are to strike on 5 and 24 July over an Olympic bonus payment, threatening disruption just days before the Games start.
The Unite union said its members will strike on Thursday July 5 and again on Tuesday July 24, three days ahead of the official opening of the sporting event.
The workers went on strike last Friday, causing travel chaos for tens of thousands of passengers and disrupting services across the capital.
The union is seeking a bonus of £500 for its 21,000 members at 20 bus companies, pointing out that other transport workers have been promised a premium payment for working during the Games.
Unite warned that bus services would come to a standstill on July 24.
Tube staff, rail workers, cleaners and staff employed on London's bicycle hire scheme are all being paid bonuses of hundreds of pounds.
Unite also announced it will go to the conciliation service Acas on Monday to show its willingness to reopen talks with the bus companies.
A previous meeting at Acas ended without a deal even though London Mayor Boris Johnson announced that £8.3 million was available to pay a bonus to bus staff.
Three firms - Go-Ahead, Arriva and Metroline - obtained a High Court injunction preventing their employees joining the strike.
Unite is re-balloting its members at the three firms for strikes, with the result due on July 17, a week before the second new strike.
Regional officer Peter Kavanagh said: "Strike action is being pushed closer and closer to the Olympics because bus companies, supported by the Mayor, seem to think it is acceptable to try a dangerous game of brinkmanship.
"This dispute could be resolved at a stroke if the operators negotiated meaningfully. Instead it looks like a co-ordinated attack, orchestrated by the Mayor, looking for a political fight with Unite and bus workers.
"The workers are getting angrier by the day, and there will be no retreat."
Unite said that as well as the £500 bonus, it would hold out for an extra £100 for every day the workers go on strike.