Catering workers at airports are balloting on possible strike action.
It would affect in-flight catering services departing from London Heathrow, Gatwick, Manchester and other airports.
It could impact flights during the busy Christmas period.
More than 700 catering services workers at dnata are voting for possible strike action.
Trade union Unite says dnata are trying to amend workers’ terms and conditions without consultation.
The ballot closes in early December.
Dnata has contracts with easyJet, Ryanair, British Airways, Emirates and other airlines.
“Dnata’s attempts to bypass its workers and force through damaging changes to terms and conditions will not be tolerated,” said United general secretary Sharon Graham.