Some customers of eir broadband and voice services are set to see the cost of their plans rise by an average of 8% from September.
The plans will increase by €6 a month the telecommunications company confirmed.
However, those using the firm's new fibre to the home products and bundles will not see their prices change.
Eir claims it is the first price increase it has implemented in four years.
"eir continuously reviews its plans to ensure they are competitive while investing heavily in the transformation of the eir network," it said in a statement.
"Originally due in 2020, this price increase was postponed due to the Covid-19 pandemic."
The company pointed to an ongoing €1bn investment it is carrying out in its fixed and mobile networks.
"This price increase will enable eir to further invest in essential infrastructure, and upgrading and maintenance of the networks," it claimed.
Eir has been the subject of repeated criticism in the last couple of years over the quality of its customer service.
The company claims it has put in place measures to rectify many of the problems, including bringing its customer support function in-house.