Ryanair's industrial relations difficulties have escalated after their pilots based in the Netherlands voted by almost 96% to back strike action.

Pilots in Ireland are set to hold their fourth 24 hour stoppage this Friday, while yesterday the German union Vereinigung Cockpit (VC) confirmed that its Ryanair members had voted by 96% in favour of industrial action.

In addition, Ryanair was forced to cancel a further 600 flights last week due to two days of cabin crew strikes in Spain, Italy, Portugal and Belgium.

In a statement, the Dutch pilots union VNV said that while negotiations with management on a collective agreement were continuing, the pilots were losing hope of a positive outcome.

VNV said Ryanair needed a "wake-up call" and that a strike in the Netherlands might be the only solution.

The union's demands include that their contracts should be governed by Dutch law, that sick pay and pension provision should be improved, and that there should be more direct employment, rather than agency or contractor recruitment.

VNV said that they supported this Friday's strike by their Irish colleagues.

Meanwhile, Ryanair Chief Executive Michael O'Leary has warned that he is prepared to move more jobs to Poland - or to cut jobs in any market if necessary - if strikes cause further damage to the company.

He was speaking at a news conference in Austria at the offices of Laudamotion.

Mr O'Leary said agreements with unions could be reached if there were common sense on their side.

It has also emerged that he has foregone his bonus for the last year of up to €950,000 because of the mismanagement of pilots' annual leave which triggered thousands of flight cancellations from September of last year.

Pilots are demanding a transparent system based on seniority for the allocation of promotions, transfers and leave.

The German pilots union VC has given Ryanair until 6 August to come up with "workable" proposals, and will hold a press conference on 8 August to announce its next move.

As yet it is unclear if the Irish pilots union Forsa will announce further stoppages.

Ryanair has invited the union to meet on Saturday or any day next week in a bid to resolve the row - provided no further strikes are called, and no Aer Lingus pilots are involved in the negotiations.

The cabin crew unions will meet over the next fortnight to agree their strategy.