Ryanair is facing the threat of pre-Christmas industrial action in three European markets, including its first ever pilots’ strike.

Pilots in Italy have voted to strike for four hours on 15 December, while colleagues in Dublin are voting on whether to follow suit, just days after Portuguese pilots voted in favour of industrial action.

Ryanair brushed off the prospect of fresh disruption, saying that previous threatened strikes hade failed to materialise.

The carrier’s relationship with its pilots has become increasingly strained after rostering problemsled to 20,000 flight cancellations.

Ryanair moved to head off the threat of Portuguese and Italian action spreading to Ireland on Thursday, warning pilots that their pay and conditions may be affected if they vote in favour of a strike.

In a memo to captains and first officers in Dublin, the Irish airline said it would freeze promotions, cut cash allowances and move pilots to different bases if they supported industrial action during ballots being held this week.

Speaking earlier this week, the Irish pilots union, IALPA, said its members were considering following their counterparts in Italy and Portugal by backing industrial action.

Capt Evan Cullen, the union’s president, said: “The pilot issues which gave rise to the flight cancellations earlier this year have not been adequately addressed. Ryanair pilots, who are members of IALPA, are currently considering their options.”

Ryanair boss Michael O’Leary. The airline does not recognise trade unions. Photograph: Niall Carson/PA

Ryanair said: “We regularly receive threats of industrial action from competitor airline pilot unions from Italy, Portugal and even Aer Lingus pilots occasionally. Both we and our pilots ignore these letters.”

The Italian pilots’ union, Anpac, which claims to represent 280 of Ryanair’s approximately 4,000 pilots, said on Wednesday its members would not work between 2pm and 6pm on 15 December.

Ryanair, which does not recognise trade unions, said Anpac was an Alitalia union with “no role” in the company. Ryanair pointed out that Anpac had previously voted to strike six times without any action taking place.

“We expect this latest threatened strike will also be postponed or cancelled,” a spokesperson said.

Relations between Ryanair and its pilots have soured since it announced two waves of cancellations due to an error in how it schedules their hours.

Michael O’Leary, Ryanair’s chief executive, admitted the airline had been “too tight on pilot numbers”. The company has been recruiting to solve the problem.

Pilots are understood to have been emboldened by a belief that the airline is still short of qualified pilots and are coordinating their efforts via their European employee representative committee (ERC) composed of current Ryanair pilots.

Ryanair deals with multiple European ERCs separately, allowing it to negotiate separate terms with different bases of operations.