In Ireland, 79 pilots based in Dublin will strike for one day on 20 December.

The airline, which does not recognise unions, said they represented about 28% of its Dublin-based captains.

Meanwhile, Ryanair pilots and cabin crew in Italy plan to strike for four hours on 15 December.

The airline said last week it would "ignore" the Italian move, claiming staff rarely heeded calls to walk out.

Pilots based in Portugal and Germany also plan industrial action.

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Cockpit, the German pilots' union, said its Ryanair members would strike for better pay and conditions if the airline refused to begin talks, but vowed not to disrupt flights over Christmas.

Ryanair said it would "not deal with or recognise" the German union "regardless of what action - if any - takes place".

Unions have long argued that their airline fails to offer pilots the same pay and conditions as its rivals.

Impact, the Irish pilots' union, said the dispute was "solely about winning independent representation for pilots in the company", said official Ashley Connolly.

The union warned of further strikes if Ryanair failed to reach agreement with its members.

"Ryanair will deal with any such disruptions if, or when they arise, and we apologise sincerely to customers for any upset or worry this threatened action... may cause," the company said.

It said the Dublin staff who planned to strike were a "small group of pilots who are working their notice and will shortly leave Ryanair, so they don't care how much upset they cause colleagues or customers".

Analysts at Goodbody said although there were deep divisions between pilots and Ryanair management, the "headlines are worse than the reality on the ground" they wrote in a note.

In September Ryanair said more than 2,000 flights would be cancelled this winter after it rearranged pilots' rosters to comply with new aviation rules.

Later that month it announced 18,000 further flights would be cancelled over the winter season, affecting more than 700,000 passengers.

Ryanair chief executive Michael O'Leary wrote to its 4,200 pilots to apologise for the changes to their rotas and urged them not to leave the airline.

However, this week it warned Dublin pilots they would lose agreed benefits by striking.

Many of the airline's pilots have joined unions following the cancellations, but Ryanair said it could legally decline to negotiate with them.