Cadbury's operations at Coolock in Dublin will face disruption next Thursday as SIPTU and Unite have served strike notice on the company.
Workers are taking action after a Labour Court recommendation, which had been rejected by union members, was being implemented.
The company - now known as Mondelez - is outsourcing the work of 17 employees based in the stores operation, which is viewed as a core function.
The unions represent 350 of the 900 employees at the plant and Richie Browne from Unite says 300 people will be taking to the picket line: