Ground handlers for Wizz Air at Luton airport are being balloted for strike action in the lead-up to Christmas.
The industrial action is being threatened over the delay of a £500 recruitment and retention bonus and would cause disruption ahead of the festive period.
The ballot, which relates only to GH London staff who are directly employed by Wizz Air and not LLA, closes on November 1.
Unite union tabled an emergency pay claim in June following the agreement of a six per cent rise and £500 retention payment in January.
The company has agreed to an extra five per cent increase and another £500 retention payment, which will also be paid to new recruits. However, Unite said the company is insisting the payment will not come into force until February 2023.
Sharon Graham, Unite’s general secretary, said: “It is out of order for the employer to sit on the payment of the £500 promised to our members.
“There’s a cost-of-living crisis and our members need every penny of their earnings.
“The retention payment needs to be introduced now, not in four months’ time, and Unite’s members have their union’s total support in this dispute.”
The union’s regional officer Jeff Hodge said: “The chronic staff shortages at GH London Ground Handling are now a safety risk.
“The company must bring forward the introduction of the recruitment and retention payment because it desperately needs to attract and keep staff.”
Menzies, employed by easyJet, and Swissport, employed by Ryanair, Tui, SunExpress, Blue Air and EL AL, are unaffected by the potential strike action.