Industrial action is also planned by Ryanair pilots in Belgium and Sweden on August 10, while German and Dutch cockpit crew have voted to strike but have not yet set a date.

Friday's strike will be the fourth in Ireland for Europe's second biggest airline, and will affect 20 out of 300 flights in and out of the country that day.

The low-cost airline in a statement on Wednesday offered to meet the Irish pilots "so we can get down to the serious work of resolving this dispute".

But its chief executive Michael O'Leary has warned the airline may shift jobs and planes to more profitable areas if the strikes continue.

"These unions have to learn that Ryanair is not some legacy airline that's going to roll over every time we're threatened with a strike," O'Leary told investors on Monday, Bloomberg reported.

Unions have been highly critical of Ryanair's combative approach.

The Swedish pilots union Svensk Pilotforening (SPF) said Ryanair "had consistently refused to meet with and negotiate with representatives of SPF", accusing the Irish airline of wanting to pick its own negotiating team from the union.

The SPF said around 40 pilots at Skavsta airport, 100 kilometres (62 miles) southwest of Stockholm, would go on strike. 

Dutch and German pilots have also voted by overwhelming margins to strike unless they reach a deal with management.

Read also: Italy fines Ryanair for mass flight cancellations

"Ryanair needs a wake-up call and a strike in the Netherlands might be the only solution," the Dutch Airline Pilots Association said in a statement.

The union said that Dutch law should be applied to Ryanair contracts and there should be "no more bogus self-employment and a sufficient sick pay and pension".

Ryanair's share price fell sharply by 3.41 percent to 13.61 euros by around 1430 GMT following the union announcements.

'Playing for time' 

Germany's Cockpit union gave Ryanair until August 6 to submit a proposal for negotiation, noting that talks last Friday had broken down with no agreement.

"Since the start of our negotiations in January, Ryanair has been playing for time and even if Ryanair is not taking this ballot seriously, industrial action like in other European countries seems unavoidable in Germany as well," the union said.

Ryanair said it remained open to further talks with pilot representatives to discuss union recognition and collective labour agreements.

"In the interim, we have requested these pilot unions to give us seven days' notice of any planned strike action so that we can minimise the disruption to our customers by cancelling flights in advance and offering them alternative flights or refunds," a company statement said.

Ryanair, which flies in 37 countries and carried 130 million passengers last year, averted widespread strikes before Christmas 2017 by agreeing to recognise trade unions for the first time in its 32-year history. 

But in the months since it has struggled to reach agreement on terms with several of them.

The airline was hit by a round of strikes last week affecting 600 flights in Belgium, Ireland, Italy, Portugal and Spain.

It said the 100,000 affected passengers had all been put on alternative flights or would receive refunds.

Read also: Tired of waiting, Ryanair passenger gets out and sits on win

Following last week's strikes, the airline threatened to cut more than 300 jobs in Ireland, blaming a downturn in bookings caused by the industrial action.

The airline said the overhaul was also partly driven by the "rapid growth" of Ryanair Sun, its profitable Polish charter operation.

Unions want the airline to give contractors the same work conditions as staff employees.

They are also seeking that Ryanair staff be employed according to the national legislation of the country they work in, rather than that of Ireland as is currently the case, which blocks the workers' access to state benefits.

Ryanair argues that since its planes fly under the Irish flag and most of its employees work on board planes, its staff are covered by Irish law.

Ryanair is Europe's biggest budget airline by passenger numbers, and the second biggest overall behind Germany's Lufthansa. 

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