A French air traffic control walkout in early July affected one million airline passengers, leading to nearly 3,000 flight cancellations and over 7,400 delays across Europe.
Ryanair claimed some French controllers extended their strike or called in sick over the subsequent weekend to gain extra leave, causing further cancellations.
The airline expressed concern that similar industrial action and sickness claims could continue throughout the summer, potentially causing more travel chaos during school holidays.
Ryanair's CEO, Michael O'Leary, criticised the EU Commission for not protecting overflights, arguing that 90 per cent of cancellations could have been avoided if they had intervened.