Almost half of Ryanair shareholders have voted against a controversial new pay package for the chief executive, Michael O’Leary, that could result in the airline handing him a €99m (£88m) bonus within five years.

A wafer-thin majority, 50.5%, approved the remuneration report at Ryanair’s annual meeting in Dublin, which means O’Leary could land the extraordinary windfall despite widespread shareholder dissent.

O’Leary’s current pay and annual bonus will be halved to a total maximum €1m a year. However, he will have an option to buy 10m shares at a fixed price of €11.12 a share, should the airline either record €2bn profit in any one year by 2024, or should the share price rise above €21. In the latter scenario, the profit on O’Leary’s share options would be worth at least €99m.

Both targets are stretching but the airline’s recent performance has indicated they could be attainable. The carrier’s share price is just under €10 but was as high as €18.60 in 2017, while Ryanair made profits of €1.45bn in 2018.

The size of the potential award “raises a red flag in terms of quantum and for our members”, said Jocelyn Brown of the UK railways pension scheme, which voted against the deal.

Speaking after the meeting, O’Leary said the pay deal was a “free bet” for investors because he would need to double the share price in order to secure the bonus. “I think most shareholders would take the view that if he doubles the share price, we don’t care what you pay him for the next five years,” he said.

O’Leary was paid a total package of €3.4m last year, including bonus and share awards. His stake in Ryanair, with 3.9% of the total stock, is worth around €400m.

Under a new company structure, O’Leary is the group chief executive of Ryanair Holdings, above four airline chief executives running the main Dublin-based European carrier, Ryanair UK, which has been hived off before Brexit, and two other subsidiaries, Laudamotion and Ryanair Sun.

About 30% of shareholders also voted against the re-election of Howard Millar – the chair of the remuneration committee – and Ryanair’s chairman, David Bonderman, who has already announced his intention to step down.

Ryanair has struggled with industrial relations in recent months and its growth plans have been curbed by the grounding of the Boeing 737 Max, delaying the first deliveries this summer of an order for 135 of the planes. As a consequence of the 737 delays, Ryanair has moved to curb expansion plans and is cutting up to 700 pilots. O’Leary said Ryanair will continue to challenge unions, whose strikes he described as complete failures.

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Pilots in the UK started a further seven days of strikes on Wednesday. Ryanair said that 96% of its flights departed on time, with any delays due to air traffic issues. The strikes had not caused cancellations, the airline said. It is bringing in contractors and flying in pilots from other European countries in an effort to maintain its services.

The Balpa union said on Thursday that Ryanair told pilots benefits would be removed should they take part in the strike, in a standoff that shows little sign of abating. Ryanair said it remained open to meeting but Balpa said Ryanair had refused to go to the Advisory, Conciliation and Arbitration Service (Acas) for talks.

Balpa’s general secretary, Brian Strutton, said: “Instead of seeking to resolve the current impasse via negotiation, Ryanair seems hellbent on prolonging the dispute by threatening pilots with the removal of staff travel benefits and inflated and draconian deductions from salary.”