Up to 320 people are set to lose their jobs at the Novartis pharmaceutical plant in Co Cork.
Management at the Swiss company announced the decision in a staff meeting at the Ringaskiddy plant on Wednesday morning.
In a statement, it said it was closing one of its production buildings at the site and would be moving a number of global services roles from Cork to centralized operations centers in Europe and Asia.
It said the decision was "strategic" and is part of a wider evaluation of the Novartis manufacturing network around the world.
Over 500 people are employed at the company's Cork site with around 700 more employed in Dublin.
The trade union SIPTU said it was seeking an urgent meeting with Novartis management.
Sector organiser Alan O'Leary, said: "Workers were aware that a review of operations was underway by senior Novartis management.
"However, the announcement today of 320 job cuts has deeply shocked the workers and their families.
"We understand that the decision to cut jobs is part of the ongoing evaluation of the Novartis manufacturing network around the world.
"It is our understanding the job cuts will occur over a period to 2022.
"We are seeking an urgent meeting with senior Novartis management in order to investigate at every opportunity to minimise the number of jobs impacted."
SIPTU added that its members were advised "a number of weeks ago" that Novartis was looking at a sale of the site in Ringaskiddy.
One worker told Newstalk: "It's as you expect, most people are worried - a lot of us are there 25, 30 years.
"It could change - these things can change - I don't hold out much hope, but it could change".
"We knew things were coming down the line, we knew things were changing in there - but they had invested a lot of money in there as well".
"It's kind of a global thing I suppose, really - it's the way the API pharmaceutical companies are going: it's smaller volume contracted out, cause they say it's cheaper".
It comes after US multinational Molex confirmed on Tuesday that it was closing its factory in Co Clare with the loss of 500 jobs.
The electronics manufacturer, which has operated out of its Shannon site since 1971, said it will close ‘in a series of phases’ from early 2020.
The company has promised to offer a "comprehensive programme of supports" to the affected workers.
Business Minister Heather Humphreys is expected to visit the area on Wednesday.
She has voiced her ‘bitter disappointment’ with the news and promised that he Government will do everything possible to assist those who lose their jobs.
She said the CEO of the company had told her that the decision cannot be reversed.
Additional reporting: Jack Quann
