More than 150 National Irish Bank staff are facing redundancy after the finance house revealed it was virtually halving its High Street presence.
NIB plans to shut down 25 out of 58 branches around the country as it merges operations in neighbouring areas.
Larry Broderick, The Irish Bank Officials' Association general secretary, warned bank bosses had not taken into account the impact of so many closures on staff and customers.
"At a time when the Government is talking about the need for greater competition in the banking industry in this country, this announcement will only serve to reduce competition and impact on customers into the future," he said.
NIB, which employs almost 700 staff in Ireland, said the closures and lay-offs would take place over the next 18 months. And despite the cuts, the bank's chief executive Andrew Healy insisted parent company, Danske Bank Group, was committed to the Irish market.
Mr Healy said: "Customers can be reassured by the fact that National Irish Bank is part of Danske Bank, a strong, well capitalised European banking group that remains ambitious for its Irish business and has a long term commitment to the Irish market. We will continue to service and support our customers. The banking sector in Ireland is on life support. Banks have to react by reducing costs and amending their business models. We are taking these actions to ensure we have a long-term future, a healthy future."
Two thirds of the redundancies will come from branch closures while the rest will be across the company. Affected staff will be offered six weeks wages for every year of service and is capped at two years' salary. Danske Bank Group is the largest bank in Denmark and a leading financial institution in Northern Europe.