Cleaning, facilities and engineering staff working on the Heathrow Express are to be balloted for strike action in a dispute over pay awards and Olympic bonuses.

The RMT confirmed today that it would be canvassing its members working as contract staff on the rail service, after a “derisory” pay increase of 1.75 per cent was tabled by their employers.

Furthermore, no incentive payments were being offered to contract staff working during the Olympic Games, the union said.

This was in contrast to the deals struck for staff employed directly for Heathrow Express, which resulted in an above inflation pay increase and a bonus of up to £700 for working during London 2012.

RMT general secretary Bob Crow said: “Here we have yet another group of contracted workers in the rail industry who are being told to take a hit on their pay and working conditions while the companies who employ them look to widen their profit margins.

“RMT members have rightly said that they will not put up with this blatant unfairness and have asked us to organise a ballot for action.”

The cleaning, facilities, asset management and mechanical engineering staff working on Heathrow Express are employed by BAA – owners of Heathrow and the airport rail link – and the contractor Amey, both part of the Ferrovial group.

A spokesperson for Amey said: “Amey is disappointed with the RMT’s decision to ballot its members for strike action, as the negotiations are ongoing.

“We are committed to avoiding any industrial action and continue to negotiate a fair employment package for our Heathrow Express employees.”

A Heathrow Express spokesperson added that any strike or action short of strike by RMT members working for Amey would not affect the running of the service.

The Heathrow Express train link operates between the capital’s largest airport and Paddington station, and carries 16,000 passengers each day.