There are fears this week's French air traffic control strike could be the start of the next wave of action disrupting Easter and summer flights and causing chaos for passengers.
When the five-day strike by staff at control centres in Brest, Bordeaux and Marseilles comes to a close later today, 1,500 flights are expected to have been cancelled, according to Airlines For Europe (A4E).
And A4E warned: "We are sure that this won't be the only strike in 2017 and we see a risk not only for Easter, but also the summer holiday season."
Airlines were asked to cut their flight offerings by 25 per cent this week, as services flying over France, including links from the UK, Italy and Spain have also been affected.
Some 800 flights were cancelled over the first two days of the week, with a further 200-300 over Wednesday and Thursday. The likes of EasyJet, Ryanair, Flybe and British Airways have all been affected by cancellations and serious detours.
Ryanair has cancelled 101 flights today, including seven to and from London Stansted.
"It’s a disgrace that so many customers are having their travel plans disrupted while the EU Commission and French government stand idly by as ATC Unions once again hold Europe to ransom," said Ryanair in a statement.
The airline has told customers to check the status of their flight on the website before travelling to the airport.
Controllers have said they are overstretched and underpaid and are taking a stand against it.
There's also a one-day Italian air traffic control strike on the cards for Monday 20 March, which would affect fewer overflights, though UK airlines flying to Italy would face cancellation and delays, while flights to destinations like Malta and Greece would have to fly detours.
Meanwhile, British Airways has been embroiled in another dispute with a week-long walkout staged by members of its cabin crew over what Unite the union has called "poverty pay". BA aid the action has resulted in a few flights being merged but that all passengers would be flown to their destinations.
Air traffic control strikes have become a repeat headache for airlines. From 2010 to 2016, there were 217 ATC strike days in the EU.
Since 2010 the overall impact of ATC strikes have cost €12bn (£10.5bn) to the EU economy.