Shiele and McDonald Mushrooms have been in operation for 17 years.
Workers were sent home from the plant in the Knockanrawley Industrial Estate on the outskirts of the town this morning.
70 jobs are to go following the closure – many of those employed there were from Eastern Europe but had been living in the area for a number of years.
Managing Director Peter McDonald says the reduction in the value of sterling following the UK Brexit vote had resulted in a major drop in their earning capacity.
The majority of the 1.5 million kilos of mushrooms grown each year by Shiele and McDonald was exported to Britain.
