Pharmaceutical company Pfizer has announced 150 redundancies at its plant in Newbridge, Co Kildare
Staff at the plant were called into a meeting with management at 8.30am.
The company said it will close its packaging operations at the Newbridge plant in 2015.
The pharmaceutical company employs over 3,200 people at a number of sites in Ireland, and said none of its other sites are affected by the announcement.
In 2010, 275 people were made redundant at the Newbridge plant in a programme that has only ended recently.
Last year, it cut 177 jobs at its facilities in Little Island and Ringaskiddy, Co Cork.
The Newbridge plant, which produces tablets and capsules, opened in 1992 and currently employs around 670 people.
Pfizer Vice President Paul Duffy has said the announcement is "no reflection" on the people of the town or their competency.
Mr Duffy said it was very difficult, but significant changes had taken place in the pharmaceutical industry which meant less people were required at the company.
He said several high-value Pfizer products including Lipitor had come off patent, meaning there was excess capacity.
There was a need to modify and change in order to take account of this.
It is understood that there is likely to be more than 150 redundancies at the plant once the closing of its packaging operation comes into effect in 2015.
Minister for Transport, Tourism and Sport Leo Varadkar has said the loss of 150 jobs at Pfizer was very bad news but he did not believe it was indicative of a greater problem within the pharmaceutical industry.
SIPTU organiser Frank Jones said the union and workers are shocked at the number of jobs being cut and the short notice given.
Speaking on RTÉ's News At One, Mr Jones said the union will meet the company at 2pm on Friday to see if there is some way of saving any of the jobs.
They will also be looking for clarity on whether the total number of job losses is 150 and what will happen at the site in 2015.
He said they have gone from programme of redundancy to programme of redundancy on this site over the past few years.
The workforce will have dropped from 1,500 to 520 by next year, he said.
He said the pool of volunteers for redundancy "has been drained" and it is the first time compulsory redundancies will have to be discussed at the site.