Workers at Dairygold are staging a one-day strike today in protest at a restructuring plan that would see more than 1,000 lay-offs.
SIPTU workers at the company's plants in Mitchelstown, Fermoy and Mallow in Co Cork and Kilbeggan, Co Westmeath, began a 24-hour work stoppage at midnight.
Dairygold says it needs to sell off its two meat plants, cut its dairy processing plants from four to two and halve its 3,000-strong workforce. Its profits have collapsed in the face stiff competition from outside the country.
About 500 people have already been laid off - almost all of them voluntarily.
The union accepts the company is in financial difficulty but says agreed industrial relations procedures have been broken by the company.
SIPTU branch secretary at Mitchelstown Ms Anne Egar said: "Management have again ignored the procedural agreement and tried to introduce unilateral changes in work practices."
The company rejects the claim, saying it has circulated a new draft agreement.