Almost 600 British Airways (BA) employees at Gatwick Airport could lose their jobs or be transferred to another company as part of plans by the airline to cut costs.
BA is proposing to shed 170 customer service and management support jobs and outsource 400 ramp worker roles.
The airline said it had begun consultation with unions over the plans.
The GMB union said the announcement was a "disaster for staff morale".
Gavin Davies, of the GMB union, said: "We will want to see proper consultations with our members on the way forward.
"GMB members want BA to take this announcement off the table to allow this to happen."
The Unite union said the plans were "extremely worrying" and called for the airline to guarantee no compulsory redundancies.
'Meet the challenge' In a statement BA said its proposals were part of a wide-ranging plan to build a stronger and more cost-competitive business and safeguard jobs for the future.
The jobs it plans to outsource include baggage, de-icing and coaching operations, and the arrivals baggage service.
The airline said it hoped to offer anyone who works on the ramp a role with a new external supplier.
BA's statement continued: "We have to meet the challenge of transforming our cost base to compete more effectively in the short-haul market, while continuing to deliver outstanding service and value for our customers."
BA is the only airline operating out of Gatwick with its own ground staff