Ryanair Holdings Plc’s Spain-based cabin crew plan to strike for four days a week over the next five months in a major escalation of a dispute over pay at Europe’s largest discount carrier. 

The SITCPLA and USO unions have called 24-hour walkouts Monday through Thursday from Aug. 8 until Jan. 7, according to a statement Wednesday. A SITCPLA representative said it had “no other option” but to ramp up protests after Ryanair fired 11 staff and began disciplinary action against 100 more.

The walkouts would be the most extensive yet in a summer of travel mayhem that’s seen thousands of flights canceled amid industrial action and chronic labor shortages even as demand recovers from the Covid pandemic. Ryanair, however, has said the unions represent only a small proportion of Spanish flight attendants and that earlier strikes had a minor impact on operations.

The last of the current walkouts at 10 Spanish airports from which Dublin-based Ryanair operates is due to end Thursday.

EasyJet Plc crew in the USO union are also embroiled in industrial action, with nine days of strikes this month, the last three of which are set to begin Friday.