Thousands of London bus workers are to be balloted for strikes in a row over payment for working during the Olympic Games.
Unite said 24,000 of its members employed by 15 separate bus operators will vote over whether to launch a campaign of industrial action.
The union has called for a £500 payment to recognise and reward bus workers for the "massive increase" in workloads during the Olympics.
Unite said the equivalent of more than 9,000 double-decker busloads of extra passengers will descend on London for the event.
With only a few months left until the Olympics, Unite said neither the bus operators nor Transport for London has engaged with the unions to plan for the Games or discuss a payment similar to deals agreed with other transport workers.
Unite regional secretary Peter Kavanagh said: "The London bus is an iconic symbol for London and bus workers will be on the front line, 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.
"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 judgment."