EasyJet has cancelled around 100 flights on Monday, including 62 from the UK, blaming higher than usual levels of staff absence due to Covid.
It said it had been trying to tackle the problem by using standby crew, but added that it had “also decided to make some cancellations in advance”.
It comes amid rising demand for travel as the Easter school holidays begin.
Airports are also facing high Covid-related absences that have led to long queues for security and check-in.
EasyJet, which is one of Europe’s biggest airlines, said the cancellations were a small part of its schedule on Monday, which is around 1,645 flights.
“As a result of the current high rates of Covid infections across Europe, like all businesses easyJet is experiencing higher than usual levels of employee sickness,” a spokesman said.
“Unfortunately it has been necessary to make some additional cancellations for today and tomorrow. We are sorry for any inconvenience this may cause.”
Affected customers have been contacted and have the option to rebook on alternative flights or receive a voucher or full refund.