British Airways axed at least 64 domestic or European flights to or from Heathrow.
Among the international routes affected were services to and from Berlin, Dublin, Geneva, Paris and Stockholm.
British Airways said passengers were given advanced warning of the cancellations.
The airline decided last month it would reduce its schedule until the end of May to limit the need to cancel flights at short notice due to staff shortages.
It has focused on routes with multiple daily flights, meaning passengers can be offered alternative departures on the same day they booked.
EasyJet cancelled at least 25 flights to or from Gatwick, affecting routes between the West Sussex airport and Amsterdam, Copenhagen, Glasgow and Milan.
The low-cost carrier said cancellations are being made “in advance to give customers the ability to rebook on to alternative flights”.
There has been a surge in demand for flights as many families have travelled abroad for the school Easter holidays, which are the first since the UK’s coronavirus restrictions for international travellers were dropped.
Airlines have been keen to attract as many bookings as possible after suffering huge losses due to the virus crisis but are struggling to cope with staff shortages.
The issue is partly caused by difficulties finding new recruits and getting their security checks processed after thousands of jobs were cut during the pandemic.
There are also high levels of coronavirus-related staff absences.
Travellers using Birmingham, Heathrow and Manchester airports have reported long queues.