Travellers arriving or departing the UK via London Gatwick – notably Canadian passengers on WestJet and British Airways – face potential disruptions to their flight plans later this month and in early August after almost 1,000 workers at the airport voted to strike in a dispute over pay.

The Unite union says that members, including baggage handlers and check-in staff, who are employed by four private contractors will walk out for four days from July 28 and again for a subsequent four-day stretch from Aug. 4.

The union said the action will “inevitably” cause disruption to flights at the height of the summer holiday season. The airlines affected are British Airways, easyJet, Ryanair, TUI, WestJet, and Wizz Air.

Gatwick is London’s second-busiest airport behind Heathrow, with a particular focus during the summer to Europe’s beach resorts in the Mediterranean.

A total of 4,410 flights are scheduled to depart Gatwick across all the strike days, equating to more than 840,000 seats, according to aviation data company Cirium.

Those involved in the dispute are employed by ASC, Menzies Aviation, GGS and DHL Services, which conduct outsourced operations for airlines including ground handling, baggage handling and check-in. Unite said it has been in negotiations with the four companies since January.

“As part of Unite’s unyielding focus on the jobs, pay and condition of its members, the union has drawn a line in the sand and is committed to eradicating the scourge of low pay at the airport,” said Sharon Graham, the union’s general- secretary.

Phil Lloyd, a senior vice president at Menzies Aviation, one of the companies involved, said Unite rejected its offer for an 11% pay rise for its ground services employees at Gatwick, which he added is on top of last year’s 10% increase.

“We are in continued discussions with our airline partners and remain committed to seeking a resolution,” he said.