Abbott Vascular Clonmel seeking 300 voluntary redundancies in Clonmel facility.
The move follows the company’s decision to streamline its cardiovascular business, putting a greater focus on science based nutritional products.
Abbott's facility at Clonmel currently employs over 1000 people.
However, the streamlining of the global operation will mean that these products will no longer be produced for the US market.
The Clonmel plant will continue to produce certain devices for other international markets.
Abbott has many manufacturing plants in Ireland and earlier this year announced an investment of €85m in its site on the Manorhamilton road, where 175 highly-skilled employees are to be taken on.
This investment is not affected by today's announcement.
SIPTU Organiser Frank Jones said there was no expectation among their members that such an announcement was imminent.
He said the "sheer number of proposed job losses will shock the workers who have given loyal and dedicated service to Abbott over many years".
Union representatives will meet tomorrow to discuss the situation with the hope of saving some jobs.