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.
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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.
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.
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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."