The SNPVAC union, which represents Ryanair Portuguese cabin crew staff, staged a strike early in April over what it says is the airline's failure to recognise Portuguese labour rights, including doctor-approved sick days.

Five unions representing Ryanair European cabin crew met on Tuesday and agreed on the deadline. Their demands include respecting national legislation where cabin crew are based and applying the same work conditions for all workers.

"If Ryanair fails to comply with these terms, the undersigned unions will initiate all the statutory and legal procedures to call a coordinated industrial action, including the use of strike action, during the summer of 2018," they said in a statement.

The unions present included Belgium's CNE/LBC, two Spanish unions and Italy's UILTASPORTI.

Ryanair's contracts in Portugal have prompted the Socialist government to look into the terms of employment. Labour Minister Jose Vieira da Silva has said that while most Portuguese crews' contracts were signed under Irish jurisdiction, the EU Treaty of Rome still guarantees worker rights under local laws.

(Reporting By Axel Bugge; Editing by Mark Potter)