European travellers are already on high alert over worries about air traffic control problems arising from both the reduced air space available due to the Ukraine war, plus staffing issues and industrial action at some locations.
"Given the scale of the industrial action, disruption, delays and cancellations are inevitable across the airport," Unite said in its statement.
Concerns over air traffic control delays already prompted easyJet to axe 2% of its summer flight schedule, mostly from Gatwick, on Monday.
On the strike-affected days, 4,410 flights are due to depart from Gatwick, equating to over 840,000 potential passengers, according to aviation analytics firm Cirium.
Britain's busiest hub, Heathrow Airport, agreed a pay deal with security workers in June, avoiding multiple days of walk-outs throughout the summer which had been planned by Unite.
Persons:
EasyJet, easyJet, William James, Sarah Young, Sachin, Mark Potter
Organizations:
Gatwick, Menzies Aviation, DHL Services, Gatwick's, British Airways, DHL, Airlines, Financial Times, Heathrow Airport, Unite, Thomson
Locations:
Ukraine, London, TUI, Gatwick, Europe