Ryanair cabin crew in Spain are set to hold three days of strikes next week amid a row over pay and working conditions.
Workers from unions USO and SITCPLA will walk out on January 8, 10 and 13, each for 24 hours, after they failed to reach an agreement with the budget airline over the dispute.
The row centres on staff in Spain being offered Irish-based contracts rather than local Spanish contracts.
The strike could affect thousands of British passengers if it goes ahead.
Ryanair was accused of “refusing to abide by the Spanish constitution” by the unions.
However, the airline has ten days to reach an agreement with staff.
A statement from the two unions said: “From SITCPLA and the USO, we hope that the company will reconsider and agree to comply with Spanish legislation.
"There is a period of ten days for the management of Ryanair to reconsider and follow, once and for all, the legality in Spain."
Ryanair have 1,800 staff based in Spain.
The strikes come just weeks after the Civil Aviation Authority decided to take legal action against the airline after it refused to compensate passengers caught up in earlier industrial action.
Ryanair was forced to cancel hundreds of flights between July and October when pilots and crew walked out over pay and working conditions.
However, the airline argued that it was not obliged to pay compensation because the strikes represented “extraordinary circumstances”.
Some passengers were left hundreds of pounds out of pocket after having to organise alternative travel plans or accommodation.
The carrier has also pulled out of the dispute resolution scheme AviationADR, which was set up to rule on unresolved complaints by passengers.
Ryanair said in a statement: "due to the efforts of the Spanish Government minimum services regulator, and the support of our pilots and cabin crew in Spain, we expect to operate a full schedule of flights to/from (and within) Spain on Tues 8th Jan."
