Guinness is set to proceed with the winding down of its packaging plant in Dundalk with the loss of 200 jobs.
The drinks giant is also planning radical restructuring of its brewing operations in the town, which will lead to a further 100 redundancies.
The company has called on the joint union forum representing its staff across the country to immediately engage in talks to ensure an orderly cessation of operations in Dundalk.
It said it still intends to close the entire Dundalk plant in favour of moving operations to Belfast and Runcorn, despite a recommendation to the contrary from a consultant appointed to examine the situation.
Guinness has already told the Labour Relations Commission that it regards the process of consultations with unions over its plans as concluded.
The company claims it will save £8m a year by moving the Dundalk packaging work to Belfast.
Unions are seeking further hearings at the LRC.