Airport check-in staff and cargo handlers at several airports in England have voted to go on strike in a dispute over pay, with a two-day action just before Christmas possible.
Unite said its members employed by Dnata at Heathrow, Gatwick and Manchester had voted by more than 4-1 in favour of walkouts in protest at an imposed 2.2% increase.
The union said supervisors were being paid a rise of 4.5%, creating a workforce of "haves and have nots".
Unite called for peace talks to avert the threat of a two-day strike on 23 and 24 December.
Regional officer Kevin Hall said: "It is extremely disappointing that Dnata has acted in such a high-handed way and sought to split the workforce between the haves and the have nots.
"Strike action is very much a last resort and our members are mindful of the potential disruption it could cause. But they feel frustrated with an employer that has refused point blank to go to Acas and negotiate in a sensible manner.
"Instead hardworking staff have seen their supervisors enjoy a pay rise double the amount that was imposed on them.
"Our members are angry over the inequality being shown within dnata and we would urge management to join us at Acas to reach a fair pay deal."
The union has around 460 members involved in the dispute, working in check-in, driving and cargo handling.
A spokesman for Gatwick Airport said: "Dnata operate only a small cargo handling operation at Gatwick. No passengers will be affected if a strike were to take place."
