London Heathrow Airport Ltd could be facing "a shock exodus of security officers", according to the Unite trade union.
The union made the warning based on what it said was "a confidential survey" of its members working at the airport.
A third of the 750 officers working at the airport, which is Europe's busiest, said they plan to quit over the next six months, with almost 50% of the workers "unsure whether they will continue to work at Heathrow".
The warning came as around 1,400 security staff at the airport continued a strike they previously warned would run through the Easter holiday.
The workers are demanding higher pay and changes to what union officials said were "gruelling" shifts.