Millions face travel chaos this summer after staff at Britain’s biggest airport announced two three-day strikes starting next week.

The Unite union said staff working for Swissport Cargo Services at Heathrow will stage the first walkout this Wednesday after the company refused to discuss a pay claim.

Air passengers face a summer of travel disruption after 275 cargo staff at Swissport Heathrow announced two three-day strikes starting from 6.30am on Wednesday, June 27 to 6.29am on Saturday June 30 and then from 6.30am on Wednesday, July 4 to 6.29am on Saturday, July 7.

Unite regional officer, Kevin Hall said: ‘Swissport has continually refused to negotiate on a pay rise for the year 2010/2011. ‘Flights could be delayed as cargo on passenger flights has to be properly configured before the plane can take-off – if cargo and vehicles are in the wrong place because of the strike this is going to have adverse knock-on effects. Swissport said in a statement: ‘Swissport Cargo Services at Heathrow Airport is aware of the proposed industrial action by members of Unite. ‘Both Swissport and the trade union are continuing discussions intended to avert the industrial action. ‘Swissport Cargo Services does not wish to make any further comment at this stage, which may compromise the outcome of the discussions.’ Last month, Swissport baggage handlers staged a four-day strike at Stansted in a row over rosters, but the company said it failed to have an impact on passengers.