The huge price hike will affect thousands of customers from next month, as the company attempts to even out differences in price with O2 Ireland bills.
Both bill pay and sim only customers will be affected by the rise.
The monthly increase, from €20.33 to €25.41, is likely to raise concerns that the operator’s recent €850m takeover of O2 Ireland may lead to higher mobile bills in Ireland.
Also, 3 Ireland may reduce some mobile data allowances for prepaid users from next month, again in an attempt to further synchronise pricing plans.
It is understood that The Carphone Warehouse and UPC will commence providing phone services in Ireland later this year, thus increasing competition in the market,