Irish-based Ryanair pilots belonging to the Irish Airline Pilots' Association and the IMPACT trade union are to hold a one-day strike on Wednesday 20 December.

IALPA, which is a branch of IMPACT, confirmed in a statement that it has served Ryanair management with notice of the strike action by Irish based directly employed pilots, most of whom are captains without whom planes cannot fly.

IMPACT acknowledged that the move would either disrupt flights or generate substantial costs to the airline.

Yesterday, the Irish directly-employed pilots backed industrial action by 94%. However, the majority of Ryanair pilots who are contractors or hired through intermediary arrangements were not balloted.

IMPACT has warned of further strikes if agreement is not reached.

Ryanair has confirmed it has received notice from IALPA of the one-day strike "by pilots directly employed by Ryanair" on 20 December.

In a statement, the airline said that, while some disruption may occur, it believes this will largely be confined to a small group of pilots who are working their notice and will shortly leave the company.

It said it had already confirmed that any Dublin-based pilots who participate in the industrial action would be in breach of the Dublin pilots base agreement and would lose benefits that arise from dealing directly with Ryanair.

IMPACT official Ashley Connolly said Ryanair's failed negotiating model had let down both shareholders and tens of thousands of passengers, whose flights were cancelled this year as "company-controlled" industrial relations proved incapable of recruiting and retaining enough pilots.

A number of aviation unions around Europe warned of imminent industrial action at Ryanair as pilots at the company intensify their campaign over negotiating and collective bargaining rights.

Italian pilots have already scheduled a four-hour stoppage between 1pm and 5pm on Friday.

Today, the German pilots' union Vereinigung Cockpit joined the campaign, warning that industrial action may spread to Ryanair pilots in Germany.

While it did not specify when that might happen, it confirmed that no strikes would take place over the peak Christmas period between 23-26 December.

In a statement, Ryanair said it had received no notification of any industrial action by its German pilots, adding that it suspects "this is more PR activity by the Lufthansa pilots group VC".

"If any such action takes place, Ryanair will deal with it head on, but we will not deal with or recognise the Lufthansa pilots union VC, regardless of what action - if any - takes place," the company added.

Meanwhile, Portuguese-based Ryanair pilots have also balloted for industrial action, but so far they have not served notice of industrial action.

Ryanair has threatened to withdraw recent pay rises and other benefits from pilots who refuse to negotiate through the negotiating structures preferred by management.

Ryanair's Chief People Office Eddie Wilson has warned that all pilots and cabin crew in Italy who are rostered for duty must report as normal for their rostered duty.

"Any industrial action taken by any cabin crew will result in the immediate loss of the five/three roster for all cabin crew at that base," Mr Wilson said.

"It may also result in the loss of the future pay increases remaining under your base agreement and no transfers or promotions within the base."

Ryanair has always insisted that it will only negotiate with Employee Representative Councils (ERCs) at each of its 87 bases.

However, pilots argue that this weakens their bargaining power and they want to negotiate collectively through a new joint European Employee Representative Council (EERC).

The situation is further complicated by the fact that a significant proportion of Ryanair pilots are not directly employed by the airline, but are contractors hired through agencies or other intermediary arrangements.

Dublin is one of the biggest Ryanair bases, with more than 300 pilots.