JET2 is contacting customers on the Balearic and Canary Islands to ask them to end their package holidays early.
Hundreds of customers have had flights back to the UK cancelled and been asked to leave sooner.
Customers due to return from Spain in early August have been told to return earlier.
However, passengers meant to be flying with the firm on Friday 31 July and Saturday 1 August are not affected - their flights are scheduled as normal.
Several families on holiday on the island of Mallorca, who were due to return next week, have told the BBC they have received emails and text messages telling them they have to return early.
Jet2 was approached for a comment.
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