The Irish airline said on Tuesday that it expects to cancel 24 of roughly 2,300 daily flights on Friday because of the action by about 100 of 350 Irish-based pilots in a strike it said was regrettable.

The pilots, who are also planning to strike on July 24, are demanding a more transparent system of pay, promotions and transfers as they aim to limit what they say is management's excessive discretion over pilots' careers.

Ryanair says it offers some of the best working conditions in the low-cost sector.

Next week Ryanair faces action in two of its three largest markets, with strikes by cabin crew in Spain and Italy, as well as in Portugal and Belgium.

Cabin crew unions in Spain and Portugal on Tuesday told Reuters the dismissal of four cabin crew in Spain last week had complicated efforts to avert two days of strike action on July 25 and 26. Belgian cabin crew also plan to strike on the two dates and Italian cabin crew will strike on July 25.

Spanish union SITCPLA said that the four crew members were dismissed after refusing to continue working after 12 hours, citing fatigue. The union said they are entitled to do this at their discretion under EU flight-time regulations.

Ryanair declined to comment on whether any crew had been dismissed, but a spokesman said that "no cabin crew have lost, or could lose, their jobs over discretion or fatigue".

A memo issued to cabin crew by Ryanair on July 11 said that a number of cabin crew had "refused to complete their duty on the uninformed assumption that they have 'discretion' (in such matters)".

SITCPLA said it had complained to the European Aviation Safety Agency and the Irish and Spanish air safety bodies and was preparing appeals against the dismissals.

"The dismissals have complicated the necessary atmosphere between Ryanair and the strike committee to restart negotiations and work things out," SITCPLA spokesman Antonio Escobar told Reuters.

The head of Portuguese union SNPVAC, Luciana Passo, also said the dismissals had reduced the chances of averting the strike, which she said she expects to involve the majority of cabin crew in the country.

The airline, which flies in 37 countries and carried 130 million passengers last year, averted widespread strikes before Christmas by deciding to recognize trade unions for the first time in its 32-year history.

But it has since struggled to reach agreement on terms with a number of them.

(Reporting by Conor Humphries; Editing by Jason Neely and David Goodman)

By Conor Humphries