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: