Travellers face a summer of holiday hell as strikes could cancel or delay a third of all flights.
More than 12,600 flights to Europe could be at risk each day as air traffic controllers walk out over pay and rotas.
Destinations affected are likely to include hotspots in Spain and Italy.
An industry source hinted initial action by Eurocontrol staff is planned when UK schools break up around July 21. More details will come on Monday.
Staff in the Union Syndicale Bruxelles want more colleagues hired.
Many quit during Covid and re-hiring has been difficult. An industry source said: “In a full-blown strike, 20 to 30% of flights would be at least delayed.”
A spokesman for Eurocontrol said: “Eurocontrol is making every effort to keep negotiations open.” Sea and rail travellers also face delays with queues at Dover caused by extra checks post-Brexit and strikes by train workers.
Stuart Wingate, the chief executive of Gatwick airport, said that potential strikes by air traffic controllers were the biggest challenge over the next few weeks.
He added that plane companies and airports had suffered because of recent, repeated strikes by air traffic controllers in France.
Mr Wingate said: “What you see with French strikes is that they affect almost every movement from the UK.”
Jo Rhodes, deputy editor of Which? Travel, said: “Travellers are understandably worried by reports that up to a third of European holidays could be impacted by air traffic control strikes.
“This summer is set to be one of the busiest in recent history, and it’s essential that airlines and airports work together to keep travellers updated of any potential issues.
“While compensation is not likely to be payable in these circumstances, airlines must fulfil their legal obligations to passengers in the event of cancellations or delays.”
The consumer watchdog advise holidaymakers to have travel insurance from the date they book their holiday and also check policies carefully to ensure it covers them in the event of cancellations due to strike action.
