Bailed-out Allied Irish Banks (AIB) is to permanently shut down 44 of its branches across the country.
The move is part of an overall plan to close a total of 67 outlets by next year.
AIB said the mass closure and amalgamation of some branches followed a review of services and was a bid to return the bank to viability.
Denis O'Callaghan, head of branch banking, said that many outlets had seen a decline in customer visits.
"We have seen a very significant change in the way our customers wish to do their banking," said Mr O'Callaghan.
"As a result of this, many of our branches have seen a large decline in customer visits. Notwithstanding this, branches will remain an important part of AIB's overall distribution strategy and will be complemented by an enhanced online service."
He said arrangements had been made with An Post to ensure people who have lost a branch in their area can carry out banking transactions at their local post office.
Customers will be able to make cash and cheque lodgements, withdraw cash and make credit card payments with the An Post service.
All customer account numbers, cheque books, direct debits, standing orders, ATM and debit cards and any credit facilities will not be affected by the closures.
The bank announced earlier this year plans to close a total of 67 branches. On top of the 44, three other outlets closed earlier this month, four are expected to shut down in November and the remaining 16 will close in 2013.