Pharmaceutical company MSD is to close its plant at Rathdrum in Co Wicklow by the end of 2015, resulting in the loss of 280 jobs.
The company told workers today of its proposed plan to cease operations at the site in two years' time.
In a statement, it said that manufacturing activities will start to be phased out in 2014, but no staff reductions are expected until the end of next year.
It said that the move comes after MSD's ongoing review of its worldwide manufacturing capabilities that has resulted in sites being sold, closed or consolidated in all regions of the world.
The plant makes ingredients for respiratory care, infectious disease and cardiovascular medicines.
As a result of the proposed closure, the company said it plans to relocate products manufactured in Rathdrum to MSD sites in Ballydine in Co Tipperary and Singapore, as well as to third-party manufacturers.
"Rathdrum has been a significant manufacturing site since 1961 and has a long history of operational excellence," according to John Smith, Site Director.
He said: "The proposal to cease operations is not a reflection of the site's performance or the highly skilled people working there.
"The proposed action is the result of MSD's ongoing review of the global manufacturing capacities needed to support its growth, business goals, product portfolio and pipeline,'' he added.
He said the firm will now enter into consultation with employees and their representatives.
IDA Ireland said it is ''committed to working intensively'' with MSD on finding a buyer for the facility and creating alternative employment in the area.
It said it will engage with Merck at a local and corporate level in the US to find an alternative owner.
Commenting on the implications of the MSD decision, IDA Ireland chief executive Barry O'Leary said the pharmaceutical sector remained a significant employer in Ireland and MSD itself will continue to employ over 2,000 people in the country.
He said that significant fresh investment in the sector is under way and several other pharmaceutical projects are currently in play and being pursued aggressively by Ireland.
However, he cautioned that the pharmaceutical sector faces several global challenges, including over-capacity and patent expiry.
Minister for Jobs, Enterprise and Innovation Richard Bruton said he is determined that "no stone is left unturned" in the search for a replacement operator for the facility.
Mr Bruton, who is on a trade mission to Texas, said his thoughts were with the workers, their families and the people of Rathdrum.
He said he had spoken to the company, which he said assured him of its commitment to Ireland.