Spanish air traffic controllers are set to commence partial strikes, disrupting flights on four days this week.
The strikes, scheduled for today, June 10, 12 and 14, will be staged for two hours each morning (10am-12pm) and two hours each afternoon (6pm-8pm).
Air traffic controllers, organised by the USCA union, are disputing penalties levied by AENA, Spain's airport operator, following a wildcat strike in 2010.
Talks aimed at averting the strikes have been unsuccessful.
Irish holidaymakers now face uncertainty and disruption, with thousands set to fly to Spain (including the Canary Islands and Majorca) over the coming week.
Under Spanish law, 70pc of air traffic control staff must be present during any strike, and USCA says it will operate to these "minimum services". But the fear remains that sympathetic workers may call in sick.
Amid the uncertainty, tourism chiefs in Fuerteventura have reserved 1,300 beds for holidaymakers whose flights could face cancellation, it has been reported.
However, airlines are hoping the effects will not be as bad as feared.
Aer Lingus plans to operate a full flight schedule on Monday, it said on its website. It has been notified of the strike, but does not anticipate "any impact to flights between Ireland and Spain."
As of this morning, Ryanair continues to advise customers on Twitter that its flights are scheduled to operate as normal, and that it will notify passengers of any changes.
Eurocontrol, Europe’s Network Manager, says it has assessed the likely level of disruption, and expects the fallout to be less severe than feared.
“After the strike, normal operations are expected and according to the Spanish authorities minimum impact is anticipated,” it is quoted as saying in Air Traffic Management magazine.
The Irish Aviation Authority has said that some flights may be affected as a result of strike action, but that any disruption to services should be limited.
More strikes are to follow on Wednesday, Friday and Sunday.
Independent Travel advises customers to contact their tour operator, travel agent or airline before travel to monitor any flight disruption, delays or schedule changes.
In 2010, hundreds of thousands of passengers were stranded when Spanish air traffic controllers staged a wildcat strike resulting in a national 'state of alarm' on the eve of a bank holiday.
In a statement on its website, USCA says it is ready to continue negotiations in the coming days to reach a solution that avoids lengthening the trade union action it is taking this week.
NB: This article will be updated as new information emerges.