Heathrow has cancelled 172 flights scheduled to depart on Monday and Tuesday, with industrial action expected to create travel chaos at the beginning of the week.

A pay dispute between the airport and its staff is ongoing but on Friday Unite said its 4,000 members, including security guards, firefighters and engineers, had rejected a revised pay offer from the airport.

The union said 88 per cent of its members had voted against the offer.

A two-day strike is planned to start on Monday, with a further 48-hour stoppage due from 23 August.

Last-minute talks to avert the action are currently being held but the airport cancelled the flights before the latest ballot result was announced.

If the walk-outs go ahead as planned, Unite said close to 2,500 staff will miss their shifts. Heathrow said passengers should contact their airlines in the first instance to see how they may be affected.

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Wayne King, Unite’s regional officer, said: “Heathrow faces a compensation bill in the region of £4.6m from airlines if the planned strikes go ahead.

“Rather than provoking the disruption that strike action will cause, we would urge Heathrow airport to use this money for an improved pay offer that better reflects the hard work of the workers who keep the airport running safely and smoothly.

“This latest vote for strike action points to growing anger among the airport’s workers in a whole range of vital jobs which are essential to the smooth and safe running of Heathrow.

“Airport bosses need to heed this latest strike vote and the overwhelming rejection by our members of the revised pay offer which offers little over and above the original offer of £3.75 extra a day for many workers.”

A Heathrow spokesman said: “We are disappointed that Unite has rejected the latest pay offer and will continue to seek an agreement at Acas.

“Unite is proceeding with its unnecessary strike action on August 5 and 6, and we regret that passengers looking to get away on well-earned breaks will be impacted by this.”

A separate pay dispute is ongoing between British Airways (BA) and its pilots, who are asking for higher salaries.

Nearly 4,000 pilots who work for British Airways and belong to the British Airline Pilots’ Association (Balpa) have voted overwhelmingly to reject a pay deal that BA says is worth 11.5 per cent over three years.

“Nobody wants the uncertainty that strike action delivers to the business,” said Willie Walsh, CEO of British Airways’ parent company IAG.

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“I think the pay offer is a fair deal.”

If talks break down, a strike could begin as early as 17 August.

The threatened strike and the scheduled Unite industrial action comes at a busy time for Heathrow, with terminals packed with members of the public jetting off on their summer holidays.