A move to seasonal production at a Banbridge dairy plant could see workers face temporary lay-offs and others lose their jobs.
Lakeland Dairies, who took over the site in May, say full operations could cease in September, resuming in March next year - though no concrete guarantees have been made.
The company is currently in consultation with staff and union representatives and management have agreed that changes will not be implemented until a 28 day period, which began on Wednesday 17 August, has elapsed.
Lakeland say an historic lack of investment in the facility, which primarily produces powdered milk, means it is only capable of producing products for which there is limited demand at certain times of the year.
"Significant investment" would be required to upgrade the technology and capacity, a spokesman said, "but this is not feasible".
The company described the developments as "very regrettable" and said it would seek to implement temporary lay-offs and potential redundancies on a voluntary basis, while it would also examine the possibility of redeployment.
However, SIPTU rep Martin O'Rourke said redeployment would likely require relocating to Co Cavan, which would be very difficult for workers, particularly those with families.
He said members had been "aware that there would be changes, some of which would be difficult" but were "shocked to be informed on Tuesday that the company intended to move towards seasonal operation of the plant.
"This will result in a large number of redundancies and only six months work a year for the vast majority of the remaining staff".
Ulster Unionist MLA Jo-Anne Dobson described the news as a "body blow" to staff, adding that the ministers for agriculture and the economy had a "responsibility and a duty" to intervene.