SIPTU and Unite members will begin a strike of indefinite duration at the Cadbury production plant in Coolock in Dublin at 7am tomorrow in a dispute concerning the outsourcing of jobs.
As part of a restructuring proposal, Cadbury - now owned by the Swiss group Mondelez International - proposed to outsource 17 jobs in its stores division.
A Labour Court recommendation which included the outsourcing proposal was rejected by Unite and SIPTU and the two unions now say they will strike until the company rescinds the decision to outsource.
SIPTU Sector Organiser John Dunne said: "Union members voted overwhelmingly to take this action following an announcement by management that it intends to unilaterally implement a Labour Court recommendation and outsource the jobs of 17 directly-employed store workers.
"The work stoppage at the plant will continue until management ends the attempt to outsource these jobs.
"The Labour Court recommendation had previously been rejected by a large majority of the 350 union members employed in the production plant. SIPTU and UNITE members proposed further talks on reducing costs and increasing flexibility in relation to the operation of the store facility at the plant.
"This proposal was rejected outright by management leaving the workers with no option but to take the industrial action that will begin tomorrow morning," Mr Dunne added.
SIPTU Manufacturing Division Organiser Gerry McCormack said: "The attempt to outsource these jobs is seen as a further erosion of the viability of the facility. It follows the movement of the production of the Time Out bar from this plant to Poland.
"Workers at the plant have over recent years agreed to the major restructuring of operations and changes in work practices," said Mr McCormack.
"However, the attempt by the management of Mondelez International to further downgrade the plant's operations has caused outrage and increased fears among the workforce about its long-term commitment to the facility," he added.
He said that had left the workforce with no alternative but to strike.
A statement from Mondelez Ireland said: "In line with many other manufacturing businesses in Ireland, both the Coolock and Rathmore chocolate manufacturing sites are under intense pressures from international competition.
"In February 2015, Mondelez Ireland presented proposals to our employees in Ireland to restructure our chocolate manufacturing business, with the aim of streamlining it to become more sustainable and competitive for the future.
"These proposals included an €11.7m investment in new chocolate making technology to enable our Coolock plant to concentrate on core chocolate brands; Cadbury Dairy Milk 8-square, Flake, Twirl and Boost, for consumption in Ireland and the export market.
"At the conclusion of a comprehensive and largely positive consultation and negotiation process, a number of issues remained unresolved and were therefore referred to the Labour Court as part of our agreed industrial relations process.
"The Labour Court recommendation was issued in November 2015 and Mondelez Ireland has confirmed that it will accept the outcome of this recommendation.
"Unfortunately, both SIPTU and UNITE Unions have voted to reject the Labour Court recommendation. A decision has now been made by both Unions to withdraw labour from the Coolock site from 7am on Thursday 3rd March 2016.
"This action is being taken in protest at the planned future outsourcing of a small number of non-core roles at some point in the future.
"The company deeply regrets that SIPTU and UNITE have decided to take this step. Any form of industrial action only further undermines the future viability of both the Coolock and Rathmore manufacturing sites and this action ultimately endangers the jobs of the c.700 people who are employed within the business.
"The management team remains available to meet again with the SIPTU and UNITE representatives to attempt to find ways to resolve this dispute and to work together on building a more sustainable future for the Coolock and Rathmore sites."