London bus drivers have threatened to take industrial action during the Olympics in a row over extra pay for working during the Games.

Members of Unite, working for 15 different bus companies in the capital, have now been balloted for a possible strike after the union called for a �500 bonus for staff on duty during the event.

Unite said Transport for London (TfL) and the bus operators had failed to engage with union leaders on a plan for the Games, despite its repeated attempts to start negotiations.

Unite cited the �600 minimum that will be handed to London Overground workers. Network Rail employees will get �500, and Docklands Light Railway staff will receive �900.

Around half of Unite members took part in the ballot.

Unite regional secretary, Peter Kavanagh, said: “Bus workers have voted to overwhelmingly support an industrial action ballot.

“The London bus is an iconic symbol for London and bus workers will be on the frontline dealing with the extra congestion and helping passengers find their way around London.

“Despite the significant extra pressure, the operators are refusing to recognise the contribution bus workers will be making to the success of the Olympics.

He added: “Every other transport worker in London is getting a payment, with the exception of the bus workers. London bus operators are doing passengers and their workers a huge disservice by refusing to engage with the union. It is a massive error of judgement.”

Leon Daniels, managing director at TfL, said staff were employed by the private bus companies.

He said: “We are disappointed at the news that Unite intends to ballot its members about taking industrial action over pay during the London 2012 Games.

“If bus drivers are required to work additional hours they are always paid overtime accordingly.”