Electronics manufacturer Sanmina is cutting up to 300 jobs at its factory in County Antrim, Northern Ireland.
The US-owned firm is relocating production from Lisburn to Hungary in a bid to cut costs.
But the company has only given staff 90 days’ notice of its factory closure.
Union leader Terry Collins from Amicus said the closure would have a “devastating impact” on Sanmina employees.
“Obviously, the ripple impact of the loss of that income which would be substantial in the locality, will have an impact, not only for the immediate employees but for the business commmunity in Lisburn,” he said.
Collins said Amicus would contact the firm to discuss the situation.
A spokesman for Sanmina said there was “no alternative” to the closure.
“This course of action is always extremely difficult,” he said. “This is not a reflection on the performance of the Lisburn employees or the management team. A great deal of effort went into preventing the closure, but there was no alternative.”