Hundreds of flights have been cancelled ahead of a 24-hour strike by Italian air traffic controllers and aviation workers on Tuesday.
Alitalia has also been forced to cancel dozens of services on Monday evening and early on Wednesday morning in addition to around 300 grounded on Tuesday.
Flights from Heathrow and London City airport to Rome and Milan are among those affected.
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The Italian flag carrier said: “Due to 24-hour Italian air traffic controllers and aviation sector strikes confirmed by some trade unions for Tuesday 25 February, Alitalia was forced to cancel several flights scheduled for that day.
“Flights set to operate on 25 February during the peak times between 7 am to 10 am and from 6 pm to 9 pm will operate as scheduled.
“As a consequence of the flight cancellations on 25 February due to the 24-hour strikes, Alitalia was also forced to cancel some flights on the late evening of 24 February and on the early morning of 26 February.
“Alitalia has taken special measures to mitigate customer inconvenience by operating bigger aircraft on domestic and international routes in order to re-book passengers affected by cancellations onto the first available flights on the same day.”
British Airways said: “We recognise the uncertainty that the strike may be causing customers, and have therefore introduced flexible rebooking options for customers booked to travel to/from Italian airports on this date.
“If you are due to travel to/from Italy on Tuesday 25 February, you can change your date of travel to any day between 23-24 February and 26-28 February inclusive.”
EasyJet said: “We are aware of planned industrial action at airports across Italy on Tuesday 25th February affecting airport, ground handling and air traffic services.
“Like all airlines operating to and from Italy, and using Italian airspace, we may see some disruption to our flying programme on this date.”