More jobs have been lost at the former Nortel plant in Monkstown, raising fears for remaining employees at the site.
US telecoms company Ciena, which bought over the bankrupt Canadian networks firm's ethernet division, has announced that 17 jobs are to be lost locally.
Following the completion of the acquisition the jobs at the repair centre have been relocated to Ciena's centre of operations in Baltimore.
The Unite union said it is now concerned the remaining 123 jobs at the site will be shifted out of Northern Ireland.
In January 140 former employees of Nortel's Enterprise division lost their jobs when the company that acquired it, US multinational Avaya, reversed its previous decision to keep the business in Monkstown.
Sean Smyth, regional Industrial Organiser with Unite, said: "Our members are reacting angrily to this announcement and are fearing the worst.
"They believe that President Obama's call on protectionism for US workers mean that more job loses at Ciena and more US-linked firms in Northern Ireland are now under major threat.
"They are demanding that the Stormont Assembly set up a jobs task force immediately to deal with the issue."
Nortel's 34-acre Monkstown facility was long held up as a beacon of the new and prosperous Northern Ireland, employing as many as 1,000 people at its peak.
However, the company went into administration in January 2009.