Ministry of Defence missile depot workers in North Ayrshire have voted to escalate strike action in a dispute over pay.
GMB Scotland members at the munitions complex in Beith, which supplies missiles to Ukraine, are set to walk out for two weeks from August 21.
The union warned the strike at the complex, which is run by Defence, Equipment & Support (DES), will disrupt shipments.
The forthcoming action comes after four days of targeted strikes in recent weeks failed to secure a resolution.
However the Ministry of Defence said the walkout will have “no effect on our ability to provide capability to Ukraine”.
The union claims that a “two-tier culture” has developed at the depot and said the pay gap between craft workers who assemble the munitions and non-craft colleagues, who support their work and prepare equipment for transport, has tripled to £18,000.
According to the union, extra payments and bonuses have been made to managers and craft workers in recent years but not to non-craft colleagues earning less than £21,000 a year.
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 number of MPs have written to Defence Secretary Ben Wallace urging him to intervene and secure resolution to the dispute, while Lesia Vasylenko, a Ukrainian MP, has urged managers to quickly negotiate an end to the row.
She said: “The work being done by GMB Scotland members at Beith could not be more important to Ukraine as we fight for our freedom.”
A Ministry of Defence spokesman said: “These strikes will have no effect on our ability to provide capability to Ukraine.
“Pre-planned contingency measures are being implemented at Defence Munitions (DM) Beith to ensure the continued safe and compliant operation of the site.
“We remain open to dialogue with GMB to discuss the issues raised and work towards resolving them.”