Ryanair's Spanish cabin crew union members plan strikes on four days of every week until January to press demands for higher pay and better working conditions, a leader of the USO union said in a statement this morning.

The strike action, which is backed both by the USO and Sitclpa union groups, will take place from Monday to Thursday during every week from Aug. 8 to Jan.7, the statement said.

Ryanair workers caused disruption at many Spanish airports during July, when they walked out for several days, mainly on weekends, during the month.

The number of cancelled flights was limited compared to other countries where Ryanair staff have also gone on strike as Spanish regulation forces airlines and staff to maintain a minimum service.

"As the company has been unable to listen to the workers, we have been forced to call new strike days," said Lidia Aransanz, a leader for USO's Ryanair section.

The unions are demanding 22 days of holiday and two extra months payment per year to comply with Spanish legislation, she added.

Spokespeople for Ryanair in Spain were not immediately available for comment.

The union said 11 cabin staff in Spain were fired during the recent strikes.

Ryanair had accounted for 22.3% of passengers traveling via Spanish airports during the first half of the year, according to data from airport operator Aena.