British Airways (IAG.L) workers have voted to strike during the school summer holidays, meaning that more than 700 BA check-in staff and ground-handling agents at Heathrow could walk out at the height of the summer season.
No strike dates have been announced, as the unions suggested that they wanted to give the airline some time to change its mind on the key issue.
GMB, the union behind the strikes, must give BA two week's notice, so the strikes could in start at the beginning of next month.
But it's understood the union will delay strikes until the third or fourth weekend in July to coincide with the start of the summer holiday getaway to maximise impact.
Heathrow has contingency plans in place to minimise the impact of the strikes, including putting managers dealing with check-ins. However, delays and possibly some cancellations could still hit travellers.
GMB has warned that holidaymakers face “a gruelling summer of travel chaos”.
Rory Boland, editor of Which? Travel, said: “Passengers must not be made to bear the brunt of these strikes. British Airways should make the necessary arrangements to avoid a raft of hugely disruptive last-minute cancellations.
“Strikes by airline staff are within the airline’s control because it is negotiating with its staff, so if your flight is delayed or cancelled because of this then you’ll likely be entitled to compensation under Denied Boarding Regulations.
"BA must also reroute customers as soon as possible using other carriers if necessary, and explain these rights to customers. We know this requirement is not always being met, so the government and Civil Aviation Authority must intervene where airlines are playing fast and loose with the rules.”
If a flight is cancelled then depending on the circumstances, passengers may be able to get a refund or compensation.
Those with travel insurance should check with their provider what they could get back.
Most passengers will also be protected by so-called Denied Boarding regulations. Under these, customers should be offered a full refund for a cancelled flight or a seat on the next available flight or one at another time.
British Airways has a site with details of rebook and refund options.
Those switching to Gatwick to avoid disruption won’t get very far as the airport announced it was putting a cap on the number of daily operations in July and August from a maximum of 900 departures and arrivals to 825 and 850 respectively.
Passengers on easyJet will bear the brunt of the cancelled flights, with British Airways, Wizz Air, Tui, Norwegian and Ryanair also expected to ground departures.
Holidaymakers have complained of long delays and queues in airports, while some have had to cancel trips altogether.