Industrial action at Glasgow Airport is to be escalated after a breakdown in talks to try and resolve a dispute over pensions.

Unite announced on Friday that a four-hour stoppage on June 14, between 4am and 8am, would be added to action already scheduled at the airport.

Members of the union voted 95% in favour, with a turnout of 75%, in April to hold strike action over spring and summer after the airport decided to close the final salary pension scheme.

The union said the decision to close the pension scheme broke an Advisory, Conciliation and Arbitration Service (Acas) agreement that was made in 2016.

The airport is part of AGS Airports Limited group, which also owns Aberdeen and Southampton airports.

AGS refuted the union claim, saying  that a copy of the agreement claimed by Unite to have been broken had been shared with staff "demonstrating this to be false".

Planned industrial action last month was suspended after "progressive talks" which saw the company table a pay offer of 3% for Aberdeen and Glasgow staff.

READ MORE: Holiday flight chaos looms as airport staff to strike

However, Unite said it has added the further stoppage in response to Glasgow Airport withdrawing from negotiations.

Two 12-hour strikes on June 7 and 10 between 4am to 4pm had already been arranged.

In a statement by AGS Airports earlier this week following Unite's notice of industrial action, the company said it had taken part in talks since January but claimed there had been "no willingness whatsoever" on the part of unions to engage in a constructive manner.

The company also said its increased offer of 3% - a rise on the initial 1.8% proposed - was a "significant improvement" in line with the demands of unions.

Its final salary pension scheme, the company said, is "simply unaffordable" with the cost to the company due to rise to 24.7% per employee.

Pat McIlvogue, Unite regional industrial officer, said: "Unite has in response to Glasgow Airport withdrawing from the negotiations over the pension scheme added a further stoppage.

"It's bewildering why AGS management seem determined to escalate this dispute. Unite entered talks in an effort to resolve this dispute, and we remain willing to talk.

"In fact, Unite invited AGS to further talks this week but this has been met with a wall of silence.

"Unless the company get back round the negotiating table, we cannot rule out further dates being added to those already announced in a dispute solely manufactured by AGS management."

A spokesman for AGS said: “We are extremely disappointed that Unite has served notice for a further date of industrial action, but would like to take this opportunity to reassure our passengers that robust contingency plans will be in place to ensure it will be business as usual at Glasgow Airport on Friday 7th, Monday 10th and Friday 14th of June.

“We have been in talks since January and, despite attending Acas, there continues to be no willingness whatsoever on the part of Unite to engage in any constructive dialogue. We made a significant improvement on our initial pay offer which was increased from 1.8% to 3% in line with demands. This was rejected by Unite without any further consultation with members and the union continues to deny them the right to make a decision on the offer of 3%.

“In regards to our final salary pension scheme, it is simply unaffordable with the cost to the company due to rise to 24.7% per employee. We tabled a generous compensation package for the remaining members, which again was rejected by Unite without first consulting its members.

“Contrary to the union’s most recent statement, no-one has made contact this week, however, as always we remain open to continuing dialogue with Unite to resolve this dispute.”