Baggage handlers and check-in staff at Gatwick and Stansted airports are to strike on Bank Holiday Monday in a row over pay.
At Gatwick, 318 Swissport workers will walk out for 24 hours, halting services at some airlines and a second strike is planned for Friday 29 August.
The staff have rejected a 3% pay offer which the Unite union said was "an insult" and well below inflation. Unite said industrial action could spread to other airports in the coming weeks. Workers at Manchester Airport will put the decision to a vote on Monday, and further ballots are expected later at Birmingham and Newcastle airports.
Unite members working for Swissport at Stansted will be joined by 30 members of the GMB union when they walk out on Monday 25 August and Friday 29. The GMB members, who work for Airfield Services screening baggage for Ryanair and easyJet, have rejected a 1.5% pay offer.
Unite has more than 300 members at Gatwick, 72% of whom voted in favour of striking. They want to see a pay increase of more than 5%. Airlines including Virgin Atlantic, Monarch, Thomson Fly and First Choice would be affected if the action later this month went ahead.
National officer Steve Turner said: "Our members are already struggling to keep up with rising food and energy costs. This pay offer is an insult to professional, hard working men and women who have to operate in extremely difficult conditions. Our members have had enough. The liberalisation of ground handling services across UK airports has resulted in a race to the bottom which must and will stop."
A Swissport spokesman said: "Swissport believes that a fair offer has been made to the unions in the light of the current economic climate that reflects the cost of living increase."
Gary Pearce, from the GMB, said the Stansted workers were due a pay rise last January but their employers had been "dragging their feet".
"These workers are doing one of the most vital jobs in the airport but are among the lowest paid," he said.