GMB Scotland members at a Ministry of Defence (MoD) munitions depot are to walk out in historic strike action on Monday.
Members at the Defence Equipment and Support (DES) depot in Beith voted in favour of strike action by 93% over a dispute on retention bonuses last month.
The union accused that managers and craft workers at the depot of receiving bonuses whilst non-craft workers do not.
The union warned that the strike action will threaten munition supplies.
GMB Scotland said it was the first time in history that DES “cannot be allowed to carry on”.
DES is an arm’s length body of the Ministry of Defence which delivers equipment and support services to the UK armed forces.
Chris Kennedy, GMB Scotland Organiser, said: “These workers are utterly vital to the UK armed forces – they deserve to be recognised as such.
“Instead, management have allowed a two tier workforce to develop, fostering bitterness and anger among workers.
“Today’s strike is the first in the history of the DES – it cannot be allowed to carry on.
“If the Defence Secretary does not step in to right this wrong, supplies of the crucial missiles manufactured at Beith will soon run low.” A Ministry of Defence spokesperson previously said: “In the event of industrial action, pre-planned contingency measures would be implemented to ensure the continued operation of the site.”