Air traffic control strikes in Europe will affect flights today and tomorrow.
Passengers flying to Milan, Rome, Venice and Lisbon will be particularly badly affected, with many services cancelled.
Airlines worst affected are British Airways, Alitalia and Ryanair. Easyjet said is has re-scheduled some flights to avoid the strike times, but there might still be an impact due to the knock-on effect of the industrial action across networks.
Ryanair has cancelled some flights from Gatwick to Cagliari, and Stansted to Bari, and warned of possible delays to other services.
Italian air traffic controllers are on strike from 13:00 until 17:00 local time; Portuguese controllers are on strike from 07:00 to 09:00 and from 14:00 to 16:00 local time.
French air traffic controllers will walk out later today until the early hours of Friday morning. Easyjet has had to cancel a small number of flights to Paris because it said all airlines operating to and from Paris airports had been requested to reduce flights by 20%.