In a statement, the SNPVAC union said that the strike warning covers all Ryanair flights for which staff are supposed to present themselves for duty between midnight on 20 August and midnight on 25 August – based on local time – and also customer assistance services or any other task on the ground.

The announcement comes on the same day that Ryanair acknowledged that it may have to dismiss as many as 500 pilots and 400 cabin crew due to the impact of the UK’s departure from the European Union, rising fuel prices and the delay in the delivery of Boeing 737 Max aircraft.

The union cited as the reason for the strike Ryanair alleged continued failure to "comply with the rules imposed by Portuguese legislation, in particular with regard to the payment of holiday and Christmas allowances, to the number of days holiday and the taking on as staff of cabin crew hired through the Crewlink and Workforce agencies."

It also accuses the company of refusing to consider the whole period of service provided through contracts signed with these temporary employment agencies and of attempting to impose a new casual employment model on these workers, rather than integrating them into the workforce.

The strike warning covers cabin crew hired by Ryanair Dac, Crewlink Ireland and Crewlink Portugal.