In Belgium, the walkout meant that only 41 percent of Ryanair flights left Charleroi airport near Brussels on Saturday and overall the budget carrier had been forced to cancel 127 flights between Friday and Sunday, an airport spokeswoman told AFP.
The situation in Belgium was further complicated by a three-day strike by Brussels Airlines staff ending Saturday that has forced the carrier owned by German giant Lufthansa to cancel 60 percent -- or some 300 -- of its flights since Thursday.
Ryanair staff staged their second day of action in Spain, resulting in flight delays but so far no cancellations.
One of the unions calling the strike said that, as of 10:00 am (0800 GMT), "there have been 15 delayed flights, both arrivals and departures.
"It is expected that this situation will increase throughout the day and tomorrow, as Ryanair's maximum profit system of leaving the minimum time between flights will cause delays," it added.
The aviation sector is struggling to recover from the pandemic, which led to mass layoffs as international travel was put on hold.
Faced with staff shortages, Amsterdam's Schiphol Airport was forced to announce earlier this month that it would be limiting traveller numbers this summer and cancelling flights.
The shortages have already caused hundreds of flights to be cancelled, while huge queues have angered travellers.
