The Molex facility in Shannon, Co Clare is set to close next year, with the loss of up to 500 jobs.
Staff were informed of the decision at a meeting with management this afternoon.
The electronics manufacturer has operated in Shannon since 1971.
However, the firm now says the site will close 'in a series of phases' - starting in early 2020, with complete closure by the end of the year.
It follows a review of the product lines manufactured at the plant.
In a statement, Molex said: "The majority of products made at the Shannon facility have insufficient financial returns and growth potential.
"Therefore, these products will either be exited or divested, with any remaining products transferred to other Molex facilities.
"The impact of this decision will regrettably result in the closure of the facility impacting up to 500 employees."
The statement adds that the company will offer a "comprehensive programme of supports" to the impacted workers.
It also notes: "The decision in no way reflects on our Shannon employees, who have made an invaluable contribution to our business over many years."
Business Minister Heather Humphreys said she was "bitterly disappointed" by the news.
She said: "My immediate thoughts are with the workers and their families at what is a very difficult time for them and for the wider Shannon area.
“I spoke to the Global CEO of the company today and expressed my deep regret at the decision, particularly given the firm’s long history in Shannon and the role its workers there have had in its success.
"He unfortunately made clear that, while the decision was made very reluctantly, it is irreversible."
Minister Humphreys insisted the Government will be "doing everything possible" to assist the impacted workers.