The European Air Traffic Control services strikes expected over the next two days in Portugal and Italy will have a significant impact on flights, according to easyJet.
The airline said it had pro-actively re-timed some flights later into and out of Lisbon in order to avoid the strike period as well as re-timing some flights to and from Milan Malpensa.
"Like all airlines flying to/ from/and over these countries, we expect it will have a significant impact on our flights during these periods.easyJet would like to reassure passengers that it will do everything possible to minimise any inconvenience for passengers," easyJet said in a statement.
British Airways (BA) have also retimed and cancelled a number of flights to and from Italy, a spokeswoman said.
"We are doing all we can to minimise disruption to customers affected by air traffic control strikes across Europe. We are advising customers on short-haul services to keep checking the very latest information on our website," said a spokesman for BA.
easyJet said the industrial action is likely to continue into Thursday with the French Air Traffic control staff taking part.
Airline passengers are likely to face travel disruption over the next two days, as strikes are expected across European Air Traffic Control services.
The strikes, due to take place in Italy and Portugal, will affect British Airways and easyJet flights to, from and over these countries. BA have said they are planning on using larger planes to help customers affected by cancellations.
The industrial action is being staged by two organisations in protest against the European Commission's Single European Sky initiative, which aims to consolidate air traffic services across the continent, NATS said.
The Air Traffic Controllers European Unions Coordination (ATCEUC) - an umbrella group that represents 14,000 members across 28 countries - is calling the strike for tomorrow, before members of the European Transport Workers' Federation (ETF) then walk out on Thursday.
Air traffic controllers in the UK will be working as normal tomorrow and on Thursday, despite industrial action being planned across Europe
I was surprised that so many of the people who would pay more for child-free flights were parents with young children themselves. I think it's unlikely that too many airlines will introduce child-free flights, because there's too much for them to lose in terms of people who would pay to fly but couldn't if they had children.
We've already seen some airlines introduce child-free zones, but a screaming baby's cry can carry quite far, so if that's the issue most people have with kids onboard then I don't know how successful they will be.
As many of 48% of parents with children aged 10 or under admitted they probably did not do their best to prevent their children being disruptive on flights, according to a survey.
The main reason for their not being more strict with offspring was that they were "on holiday" so were more likely to let their children do what they liked, the poll by travel agent sunshine.co.uk found.