Bord Na Móna are due to lay off 150 employees from their Lough Ree Power plant in Longford.
78 seasonal employees will be laid off with immediate effect and 72 permanent employees will be put on temporary unpaid lay-off from next Thursday.
A spokesman for the company says it "will provide regular updates to all employees."
RTÉ reports that the job losses are due to "legal proceedings against the plant taken by the Environmental Protection Agency".
The ESB said in a statement that a decision to close the plant was made on July 5.
Explaining the reasoning behind the decision, the ESB said:
"ESB is required under its license to return cooling water from Lough Ree Power back into the River Shannon in such a manner so as not to raise the downstream river temperature by more than 1.5 degrees Celsius above the upstream intake temperature.
"A new condition imposed by the EPA some years after the station was commissioned required this condition to be applied over a smaller cross-section of the river.
"While the station normally complies with this obligation, there are specific times of the year where low flow in the river can give rise to brief excursions above this limit.
"ESB commissioned a study to identify a range of engineering options to satisfy this condition at all times and none of these options were deemed feasible."