The industrial dispute at Aer Lingus escalated on Friday as pilots announced an eight-hour strike on Saturday June 29.

A previously announced, indefinite work-to-rule from Wednesday June 26, which would mean pilots would not engage in overtime or out-of-hours duties, saw the airline cancel 124 flights.

Aer Lingus said this will affect about 20,000 customers over the five days from the Wednesday as it pledged to accommodate people amid the busy summer holiday season.

About 30 minutes after Aer Lingus announced the flights that would be affected by the work-to-rule, a strike was announced by the pilot’s union for June 29, running from 5am to 1pm.

The Irish Air Line Pilots’ Association (Ialpa), which represents the pilots, said they had been “forced” to escalate the dispute following “a campaign of antagonism by Aer Lingus management”.

The president of Ialpa, captain Mark Tighe, claimed that the airline had sent “threatening” letters to association members.

“The scale of next week’s anticipated flight cancellations, as described by Aer Lingus, illustrates the extent to which the company relies on the flexibility and goodwill of pilots,” he said.

“We go above and beyond to provide a good service to our customers. The company has recently enjoyed a 400% increase in profits, which demonstrates how much the company benefits directly from that flexibility and goodwill.

“As always, Ialpa remains open to talking with Aer Lingus in direct negotiations to settle this dispute in a way that fairly deals with pilots’ pay.”

Aer Lingus condemned the planned strike action and said it was “appalled” that Ialpa would escalate the dispute, which it said was “clearly designed to inflict maximum damage on passenger’s travel plans”.

“Aer Lingus will assess the impact of this notice of strike action and do everything we can to minimise the further disruption this will cause to passengers,” it said.

Donal Moriarty, chief corporate affairs officer at Aer Lingus, said earlier that the work-to-rule form of industrial action “gets worse day by day” so there was a risk there would be further cancellations.

He told RTE Radio: “What will happen over the next couple of days is that impacted passengers will be contacted and advised of cancellations if it affects them and then given their options in terms of refund, re-accommodation or voucher.”

The airline said it had automatically rebooked some customers on to alternative flights and has begun emailing all other customers informing them of the cancellation and advising them of their options.

People who are worried about their flight being cancelled have also been given the option to cancel or rebook their flights for a later date for free.

The list of cancelled flights is available on the “travel advisory” section on the Aer Lingus website.

Ialpa is seeking a pay increase of 24%, which they say equates to inflation since the last pay rise in 2019.

Aer Lingus has described the pay demand as unrealistic and said there have been no pay deals in Ireland that delivered such an increase.

Irish premier Simon Harris said people need to “step back from the brink” in relation to the dispute.

“The Government has a willingness for parties to come together through the Government’s industrial relations mechanisms, and they are available to all of the parties and I would encourage parties to it,” Mr Harris said on Friday.

“People need to step back from the brink in relation to this.

“Of course, anybody has a right in their workplace to highlight an issue, I get that. But what I do not get is the fact that at this time of the year, when people in our country are about to go on their summer holidays, people who’ve worked hard and saved up throughout the year are about to be seriously discommoded by this action.

“I don’t think there is a justification for that, quite frankly, in terms of the impact it will have.

“The impact is disproportionate and … people need to step back from the brink.

“This will affect children and parents looking to go on holidays. It also affects business and will also affect people coming into our country, too, in terms of tourism at these busy times.

“Disputes only ever get resolved by engagement, that’s how they always end up being resolved. The question for both parties now is, will they try and resolve it and show a maturity in relation to this, or are they going to allow this to trundle on and then ultimately end up in talks.

“Talks need to happen. What I’m asking is now we shorten the protracted process and all the chaos that would ensue for people and actually get around the table quickly.”

Mr Moriarty said: “We would like to engage in direct discussions with Ialpa to reach a reasonable settlement to this pay dispute and we are trying to do that but, unfortunately, Ialpa ended those discussions last Monday.”

He said Aer Lingus pilots are already paid “very well” and their salaries are “in line” with the market rates.

“There is a pay deal on offer to them of a 12.25% increase, which they’ve declined,” he said.

“We have also tried to discuss with them building upon that over and above 12.25% by discussing improvements in productivity and flexibility, but unfortunately Ialpa have been unwilling (to engage) with those discussions.”

About a quarter of all Ialpa members are on the top pay package of about 287,000 euro, which includes the value of pensions and other benefits.

To reach this pay package takes 26 years and several exams, representatives have said.