Union leaders will restart talks with Heathrow on Sunday morning as the airport attempts to avert strikes by thousands of workers at the peak of the holiday season.

Heathrow has already cancelled 177 flights for on Monday and Tuesday because of a planned 48-hour stoppage by members of Unite.

Faced with imminent industrial action, Heathrow management held a meeting, chaired by the conciliation service Acas, with union leaders on Saturday, after discussions had continued without agreement until 11pm on Friday. But the talks were adjourned on Saturday night after Unite rejected a revised pay deal.

“Unite have rejected our revised pay offer today. While we are disappointed, we will continue to seek an agreement at Acas tomorrow,” the spokesperson said. The talks are due to resume on Sunday at 10am.

But there was widespread anger from passengers who were not told which flights had been cancelled.

A Heathrow spokesman said: “Airlines will confirm with passengers what flights they will be consolidating and cancelling.

“We have activated contingency plans which will keep the airport open and safe on both strike days. We expect security queue times to be longer than normal and advise passengers to check our website for detailed information on how to prepare for their flights and when to arrive at the airport.

“We advise passengers to contact their airlines for the latest information, as well as follow our Twitter and Facebook accounts for further updates.”

About 4,000 Unite members voted by almost 9-1 to reject a pay offer which Heathrow said was worth 7.3% over two and a half years.

Wayne King, Unite’s regional coordinating officer, said: “Airport bosses need to heed this latest strike vote and the overwhelming rejection by our members of their revised pay offer, which offers little over and above the original offer of £3.75 extra a day for many workers.

“It is in Heathrow bosses’ power to settle this dispute. We would urge them to work with us to do so, and avoid the disruption to passengers that strike action will inevitably bring.”

Further strikes are planned for 23 and 24 August.