Representatives of workers at three Lakeland Dairies sites in Monaghan and Down that are earmarked for closure are to meet the co-op's management to discuss the decision.
SIPTU said the threat to the 78 jobs at the locations had left the workers and families in shock.
"The company has cited the creation of further processing efficiencies and the evolving environmental realities and regulatory direction in milk supply as the driving force for the proposed closure of these long-established dairy manufacturing facilities," said Denis Gormalley, SIPTU Agriculture, Ingredients, Food and Drink (AIFD) Sector Organiser.
"When we meet the company, we intend to examine and interrogate this rationale as we explore all possible alternatives."
The union said it would leave no stone unturned in its quest to save as many jobs as possible.
Yesterday Lakeland Dairies said its liquid milk production plant in Coolshannagh in Co Monaghan is to shut in the first quarter of 2025.
This is the result of a plan to transfer liquid milk production from there to Lakeland Dairies in Killeshandra, Co Cavan and additional bulk milk handling activities to other sites.
Following the ending of production in Coolshannagh it is expected that the Monaghan site will be sold.
Currently it is understood that around 50 people are employed in the facility.
Separately, milk drying facilities at Lough Egish in Co Monaghan, where over 20 people work, are also to close in June of next year.
Instead, milk will continue to be processed at Lakeland Dairies Bailieboro, Killeshandra, Newtownards, Ballyrashane and Artigarvan.
However, the Lakeland Agri feed and inputs operation at the neighbouring Lough Egish feed mill will continue to grow and develop.
Another Lakeland Dairies site in Banbridge, Co Down, which has acted as a butter churning and packing and powder storage site, will also close in June 2024 and be sold.
Two employees work at that facility.
