Lakeland Dairies is to let go nearly 70 staff in Co Monaghan.
In April, the Cavan company merged with LacPatrick Dairies, which is based in Monaghan town.
The company says LacPatrick had significant losses before the amalgamation.
To reduce costs, it has decided to make 68 of the 130 staff in Monaghan redundant.
Some of the staff will be redeployed.
Sinn Féin MEP Matt Carthy, who lives in Monaghan, says it's a huge blow for Co. Monaghan and the local economy.