Tara Mines in Co Meath has announced it's to temporarily lay off 650 workers.
The company which runs the facility in Navan, says the decision was taken to safeguard its long-term future.
Boliden Tara Mines says operations are to be temporarily suspended within the next four weeks.
Employees were told at a meeting last night it's in response to significant and unsustainable financial losses.
Enterprise Minister Simon Coveney, says State agencies will be sent to the mine today to assist those affected.
Minister for Social Protection, Heather Humphreys, confirmed in a statement last night that "a dedicated team from the Department of Social Protection is being put in place to provide support to the impacted workers and their families".
Gunnar Nyström, General Manager of Boliden Tara Mines said: “In the long-term interest of Boliden Tara Mines, we have taken the decision to temporarily suspend operations and place the mine into care and maintenance. Regrettably, this will mean that up to 650 employees will be laid off temporarily.
In a statement last night, the company said, "The business is currently cash-flow negative and the losses have been brought about by a combination of factors that have made this decision unavoidable. These factors include operational challenges, a decline in the price of zinc, high energy prices, and general cost inflation".
Michael Fitzgerald, a miner and shop steward at Tara Mines, says the news was communicated poorly to staff.
" It came as a massive shock. We were very disappointed with the communication from the company.
"Many workers heard it from the nine o'clock news last night. We will be exploring as a union, all alternatives to going into care and maintenance before all production will cease.
"It'll be just keeping the pumps going, a minimum crew just to keep the place ready from when we can go back".
Tara Mines is the country's largest zinc mine and has been in operation since 1977. Boliden acquired the mine in 2004.
