Flights to and from Portugal face five days of disruption due to strike action by air traffic controllers.
The first walkout started for two hours this morning and other strikes have been called for tomorrow, April 19, 20 and 26.
The industrial action is scheduled to run between 7-9 am on each day.
The Foreign and Commonwealth Office said: “Be prepared for delays and keep in touch with your airline or tour operator for advice on the options available to you.”