Eir has announced plans to cut 750 staff. In a statement, the telecoms company said employees will leave as part of voluntary redundancy scheme.
The firm has stressed that the job losses will not impact in the roll-out of broadband in rural areas.
"This has been launched in an effort to deliver costs savings and create a leaner, more agile organisation", a statement explained.
The company said "eligible staff have already or will shortly receive correspondence with a personalised financial estimate for their consideration."
However, Eir said many of its workers will not be eligible to put themselves forward for redundancy.
A number of trade unions have said they will work with the company to make sure their members leave on the best possible terms.
Steve Fitzpatrick, General Secretary of the Communications Workers' Union, said he had no reason to believe the lay-offs will be "anything other than voluntary".
"We will engage with the company on the detail and, in particular, to ensure that proper arrangements are put in place to cover work once the scheme takes effect", he said.
The announcement of job losses comes just days after a telecoms billionaire behind two French companies bought 65% of Eir.