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;
In a statement released on behalf of Mondelez: "The company regrets that SIPTU and UNITE has taken this step and has again re-affirmed its acceptance of the proposals contained in the WRC recommendations including 4% pay increases for all impacted staff.
"In line with many other manufacturing businesses in Ireland, the Coolock chocolate manufacturing site is under intense pressures from international competition and any form of industrial action only undermines the future viability of the entire site.
"We remain available to meet again with the SIPTU and UNITE representatives to attempt to find ways to avoid this proposed industrial action whilst also building a more sustainable future for the Coolock site."
