Industrial action by Ryanair cabin crew in Europe in June and July could add to the issues plaguing the travel industry this summer.
Belgium are the latest to announce plans to strike that could affect UK fliers, with the earliest date set for this Friday, June 24.
They join cabin crews in France, Italy, Spain and Portugal who have confirmed strikes set during the busy summer holiday season.
The strike in Belgium is another blow for the budget carrier which operates 17 planes from Charleroi and two aircraft from Brussels.
More than 60 percent of flights to and from Belgium operate on aircraft that are not based in the country with plans originating from other nations operating routes.
At the centre of the disputes are wage levels and pay for pre-take-off and post-landing duties, Wales Online reported.
UK cabin crew have not voted to strike, but the dispute could potentially affect thousands of holidaymakers.
Unions said they were planning to walkout in Belgium and Portugal from June 24-26, a strike in France from June 25-26, and in Italy on June 25.
They also announced plans for a strike in Spain on June 24-26, June 30, and July 1-2.
A Ryanair spokesperson said last week the unions should return to the negotiating table to deliver improvements instead of disrupting passenger travel plans.
Ryanair boss Michael O'Leary had said union accusations were "complete rubbish".
He went on: "We fully comply with Belgian law, we have labour agreements here with both the pilot unions and the cabin crew unions."
Here is the latest on the walkout plans:
Belgium
Trade unions claimed they were forced into action because Ryanair was not respecting Belgian labour law covering such issues as the minimum wage or pay of cabin staff.
Unions representing Ryanair workers in various European countries said on Friday that they were planning a strike in Belgium from June 24 to June 26.
Portugal
Portugal-based cabin crew have said a three-day strike will go ahead on June 24, 25 and 26, which could impact dozens of flights between the UK and the popular holiday destination.
Workers are demanding compliance with Portuguese law and better working conditions, Portugal's union of civil aviation personnel SNPVAC said in a statement.
"This mobilisation is not only an opportunity to put the spotlight on multiple attacks on workers' dignity and to make this reality known but also a moment to show unity and solidarity against dumping", the union added.
Spain
The strike in Portugal comes just one day after Ryanair's Spanish cabin crew announced a six-day strike.
The action will take place on June 24, 35, 26 and 30, and on July 1 and 2.
Workers have blamed discontent with working conditions and pay as the reason for the series of walkouts.
Italy
Unions representing staff in Italy called for a 24-hour strike on June 25 to coincide with walkouts in both Spain and Portugal.
Unions FILT-CGIL and UIL Trasporti said they sought improved pay and conditions after staging a four-hour stoppage earlier in June.
France
Union members employed by the no-frills airline in France have threatened a walkout on June 25-26 adding to the disruption for travellers across Europe.
Flights from Toulouse, Marseille and Paris Beauvais airports to Morocco, Italy, Spain, Portugal, Greece, Corsica, England, Scotland and Ireland are likely to be affected.
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