IRISH Nationwide mortgage holders face an interest rate hike adding €30 to monthly repayments for every €100,000 borrowed from tomorrow.
The lender is set to become the sixth to increase the mortgage interest rate it charges existing and new customers, reports said today.
Its rate on standard variable mortgages will rise by 0.54pc tomorrow.
EBS and Haven have also hiked the rates charged to those who opt to take out fixed rate mortgages.
The Irish Nationwide rise comes despite the European Central Bank earlier this month leaving its benchmark interest rate unchanged at 1pc for the 15th consecutive month.
It's the second time this year that the building society has hiked its standard variable rate.
Around half of the society's residential mortgage holders are on standard variable rates, with another 30pc of its domestic mortgage holders on other types of variable rates which are also rising by 0.54pc.
Head of mortgages Martin Noonan admitted that this meant the rate hike would impact on around eight out of 10 of its residential mortgage borrowers.
The building society, which has the lowest rate in the market for those who want to fix their rate, is also changing the way it prices fixed-rate mortgages.
The move will make it more expensive to fix for those whose mortgage amount is high compared with the value of their home, financial observers said.