Nearly 80 jobs are to be lost in Boyle, Co Roscommon, with the closure of a fish-breading facility by Green Isle Foods.
The decision to close the plant by early September, and move production to Britain, was announced by the company yesterday.
It said the move, which will result in 78 redundancies, was necessitated by "production efficiency measures" aimed at maintaining the company's leadership position in the highly-competitive frozen fish market.
A consultation process with employees began yesterday.
The Boyle plant is part of Green Isle's Irish business which produces the Donegal Catch brand of fish products.
Primary processing, procurement, quality control, R&D, sales and marketing, and brand development will continue unchanged at Green Isle's operations in Gurteen and Naas.
The company's managing director, Kieran Carolan, said the decision to close the Boyle facility followed an extensive review of costs.
"The fish business continues to be successful, employing over 120 people in Ireland. However, we have taken this regrettable but unavoidable decision, and this action positions the business for the long-term on a more competitive footing."
Mr Carolan said the transfer of the breading process to a UK facility within the Green Isle group would provide it with much-needed scale which was not possible at Boyle.
"The move will protect the remaining jobs and ensure the long-term competitiveness and sustainability of the business and our key Donegal Catch brand."
He said every effort would be made to help workers affected by the closure decision to secure retraining and employment.
"We firmly believe this decision is in the best interests of securing the future of Green Isle's fish business and its employees."
Green Isle, which is part of Northern Foods' frozen division, has headquarters in Naas, Co Kildare, and employs more than 1,300 people in Naas, Portumna, Longford, Gurteen and Boyle.
Meanwhile, Bausch & Lomb have announced the loss of 41 jobs at its contact-lens manufacturing facility in Waterford.
A spokesman yesterday said the company would be "rebalancing its workforce" over the coming weeks by reducing the number of temporary jobs at the plant.
The news follows an announcement on Monday that 135 jobs would be lost if the NTL call centre in Waterford were closed as planned.
Management of UPC Ireland, the new parent company of cable groups NTL Ireland and Chorus, confirmed that the job cuts would be effective from September through to March 2007.