Workers at a munitions depot which provides missiles to Ukraine will strike for two weeks after accusing the Ministry of Defence of “bad faith”, a union said.
Around 50 members of GMB Scotland at the MoD’s Defence, Equipment & Support centre in Beith, North Ayrshire, will walk out on Monday.
The union said strike action was voted for over allegations of a “two-tier” workplace, with an £18,000 pay gap between workers who are known as “craft” or “non-craft”.
The GMB accused the MoD of “bad faith and disrespect” after talks with conciliation service Acas collapsed.
Craft workers assemble the munitions, while non-craft colleagues support their work and prepare equipment for transport but receive no extra bonuses or additional payments.
Some non-craft workers earn less than £21,000 a year, and the pay gap is said by the union to have tripled in recent years.
The GMB said 93% of members at the depot voted for strike action in July over a dispute on retention bonuses.
Strikes took place across four days in early August, but two weeks of walkouts planned from August 21 were postponed for the Acas talks.
Lesia Vasylenko, an influential Ukrainian MP, has thanked staff at the site for their “life-saving” work.
She previously said: “The work done by GMB Scotland members at Beith could not be more important to Ukraine as we fight for our freedom.”
The Confederation of Free Trade Unions of Ukraine has also voiced support for the workers.
GMB Scotland organiser Chris Kennedy said: “We suspended our action in good faith to allow these discussions to go ahead.
“We had been assured decision-makers would be arriving with constructive proposals to resolve this dispute but they didn’t and there wasn’t.
“There was nothing new to discuss and nothing new to take back to our members.
“If the Ministry of Defence was advised this was how to proceed, it was badly advised.
“It was, in fact, an exercise in bad faith and disrespect and has only hardened our members’ determination to secure fair pay.
“They do not want to strike but have been given no choice.”
GMB Scotland secretary Louise Gilmour said: “A two-tier culture has been allowed to embed itself in this workplace and risks good working relationships now and in the future.
“Our members are doing important and responsible jobs and simply want that work to be fairly recognised.
“Instead, they have seen the gap between their salaries and that of their colleagues stretch wider and wider.
“Everyone brings different skills to their work and that should be recognised, but the role of our members is fundamental to the effective operation of this important site.
“They are only asking for fairness and the support they have received from Scotland to Ukraine shows why they deserve it.”
A Ministry of Defence spokesman said: “The proposed strike will have no effect on our ongoing support to Ukraine.
“Defence Equipment & Support (DE&S) has well-established contingency plans in place to mitigate the impact while also ensuring all activities are carried out safely and securely by appropriately trained employees.
“DE&S management has put forward an offer which would significantly improve the pay of the workers in dispute in a sustainable and affordable way.
“The DE&S reward framework is designed to be fair and equitable and to recognise the knowledge, skills and experience employees bring to their roles.
“As with all employers, employees are paid differently depending on grade as well as the nature of their role.”