EasyJet pilots could stage a walk-out over October half term sparking travel chaos for families.
A staff ballot on whether to carry-out industrial action will end on September 21, the pilots union Balpa said.
In a letter to pilots leaked to The Daily Telegraph, the union blamed a "dispute with easyJet purely concerning pilot fatigue" for potential strikes.
If pilots vote in favour of a strike, action could take place at any time after the ballot closes and could coincide with school’s October half-term holidays.
In its letter to pilots Balpa said the union had “been forced to take such extreme measures".
It added: "The core issue of the dispute was that fatigue had risen year on year, to levels pilots and Balpa find unacceptable."
The airline, which has around 2,000 UK-based pilots, said pilots' workloads were set by the Civil Aviation Authority.
A spokesman for easyJet said: "Although Balpa has informed us they are balloting their members, easyJet and Balpa continue to work together.
"We still hope to reach a mutually agreeable solution".
EasyJet operates in more than 30 countries, flying to popular holiday destinations such as France, Italy and Spain.
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