* Italian union says to strike Dec. 15
Portuguese pilots vote for action
* Irish pilots to vote this week
* Ryanair says would cut pay, freeze promotions (Adds Ryanair memo to pilots)
By Conor Humphries
DUBLIN, Dec 6 (Reuters) - Ryanair will cut the pay and conditions of pilots at its Dublin home base if they vote for industrial action, the airline said on Wednesday as an Italian union said its members would hold the company's first-ever strike next week.
The Irish airline, Europe's largest by passenger numbers, is trying to recover from a damaging wave of cancellations caused by rostering problems, while pilots at less than a third of its 87 bases have accepted an offer to increase pay.
Italian union ANPAC, which said the planned strike on Dec. 15 would last for four hours, is one of several across Europe that have been preparing for industrial action over demands for better conditions and an overhaul of Ryanair's collective bargaining system.
Ryanair has never been subject to a pilot strike, although baggage handlers took industrial action briefly in 1998 and does not recognise trade unions. A spokesman said it did not believe the Italian pilots would actually strike.
The airline sent a memo to Dublin pilots on Wednesday saying it would freeze promotions, cut cash allowances and possibly move pilots to alternative bases if pilots working out of Dublin support industrial action at ballots on Wednesday and Thursday.
The memo said Ireland's IALPA pilots union had demanded recognition, a move which Ryanair said "simply will not happen".
A Ryanair spokeswoman said the company "did not comment on communication with our people."
"NO ROLE" FOR UNIONS
Italy's ANPAC, which said it represents 280 of Ryanair's approximately 4,000 pilots - and 40 percent of those based in Italy - said Ryanair pilots and cabin crew would not work between 1400 and 1800 GMT on Dec. 15.
Air traffic controllers and other airline workers will also strike on the same day, the union said.
The spokesman for Ryanair said ANPAC had "no role in Ryanair" and that the strike was the sixth that it and other Italian unions had announced before later being cancelled.
"We expect this latest threatened strike will also be postponed cancelled," the spokesman said.
Pilots have mobilised in the wake of the announcement of 20,000 flight cancellations by the Irish carrier, which it blamed on a lack of standby pilots due to a failure in rostering following a rule change by Irish regulators.
Chief Executive Michael O'Leary told investors in September the airline had probably been "running too tight on pilot numbers" and the airline has since launched a hiring drive.
Ryanair routinely dismisses "competitor pilot unions" who it says claim to represent more Ryanair pilots than they do. But several unions in recent weeks have formed company councils and named serving Ryanair pilots as members.
Portugal's SPAC trade union this week announced that its members, which it says include a majority of Ryanair pilots based in the country, had voted to give it a mandate to call for industrial action up to and including a full strike.
O'Leary told pilots in September that there would be "consequences" for any pilots who take industrial action and that some aircraft could be taken out of bases if it were to occur. (Reporting by Conor Humphries; editing by Louise Heavens and Alexander Smith)