The Financial Services Union has described Bank of Ireland's decision to close branches across the island of Ireland as shameful and an act of betrayal to loyal staff and customers.
The FSU said the move will hurt vulnerable people the most.
It called on the Central Bank of Ireland and the Minister for Finance to act now to protect customers and staff.
"The announcement this morning by Bank of Ireland to close 103 branches will shock both staff and customers alike," said John O'Connell, General Secretary.
"How can Bank of Ireland think it is appropriate to make this announcement when the country is in the middle of a pandemic. It is a shameful act which needs to be reversed," he stated.
He said Bank of Ireland could not be allowed to withdraw a vital service from the elderly, from people with no internet access, from people with literacy problems at this time of increased anxiety.
Mr O'Connell also said staff in the bank had worked tirelessly through the Covid-19 pandemic to provide a professional service.
The FSU said the decision will also massively impact on the SME sector at a time when it is on its knees.
The union has called for a moratorium on branch closures at least until the end of 2022.
Speaking on Morning Ireland, John O'Connell said that branches are being closed in areas with poor broadband and little access to other services.
Mr O'Connell said the FSU believes the future of banking is blended banking (online and branch network) and it is important that there is a public debate on the issue before this is "implemented over our heads without agreement."
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He said the FSU will assure staff that it would protect their jobs and campaign against the Bank of Ireland closures.
The union is not against change, he said, but people needed to be treated with respect.
Seamus Boland, chief executive of Irish Rural Link, said he was extremely disappointed with the Bank of Ireland decision and warned that "we are heading to more and more closures."
Mr Boland said this is another blow to rural areas and other non rural areas.
He pointed out that there have been a number of post office closures in recent years and said the idea that there will be a post office branch to pick up the slack is "difficult, if not impossible" to imagine.
In addition, Mr Boland said that transferring the bank business into a post office needs "a lot more than simply using the same collection point".
He pointed out that many post offices are not equipped for much more than taking money across the country and many are not suitable for dealing with problems on the account.
For that, he said, you need the privacy of a bank.
SIPTU said its members were shocked to hear that Bank of Ireland has announced the closure of 103 branches in its branch network.
SIPTU's Peadar Nolan said the closures have come as a complete bolt out of the blue and at a time when staff have been working tirelessly during the Covid-19 crisis to ensure the network is operational and kept open for customers.
"We are calling on the bank to halt any plans to close these branches, particularly while staff and customers are trying to cope during the pandemic," Mr Nolan said.
Mr Nolan said the union is seeking an immediate meeting with management to discuss this decision and will be seeking alternatives to the plan.
"We also want the Minister for Finance, Paschal Donohoe, to intervene and protect the interests of staff and customers," he said.
"This really is a major shock for our members some who have been with the bank all of their working lives. The uncertainty created by this announcement is devastating," he added.
Trade union Unite said that the decision by Bank of Ireland to close branches across Ireland is a blow not only to the workers who have built the bank, but also to local communities who depend on local banking services.
Jean O'Dowd, Unite Regional Officer said she is "shocked" that the bank would take such a decision during a pandemic.
"This decision makes a mockery of Bank of Ireland’s standing as a so-called 'pillar bank’, and is a slap in the face not only to the bank’s loyal workforce, but also to the Irish taxpayers who bailed out the bank to the tune of €4.8 billion following the financial crash.
"Unite would urge Bank of Ireland to put any decision regarding branch closures on hold pending a full and transparent consultation process involving all stakeholders", Ms O’Dowd added.
In a statement the Department of Finance said it noted the bank's decision.
It said it welcomes the bank's announcement that it has agreed a new partnership with An Post which will allow personal and business customers use their local post office for a range of banking services.
But ultimately it added that the bank's decision to close branches is a commercial matter and is solely the responsibility of the Board and management.
Sinn Féin's Finance spokesperson Pearse Doherty described the closures as "the wrong decision at the wrong time" and called on the Minister for Finance to come out publicly to ask Bank of Ireland to halt these plans and to announce the establishment of a forum on the future of banking".
Speaking on RTÉ's Today with Claire Byrne, Pearse Doherty said the Minister for Finance, as one of the largest shareholders in Bank of Ireland, "has a responsibility here".
Mr Doherty said he "completely supports" the call from the FSU to have a ban on bank closures until the end of 2022.
He said Bank of Ireland "is tone deaf to the fact that we're in the middle of a pandemic" and that it is "rich that Bank of Ireland are using the statistics from the pandemic to actually make their case".
He said some services, including foreign currency lodgement and mortgage applications, will not be available in post offices.
Meanwhile, Labour's Finance spokesperson Ged Nash described Bank of Ireland plans to close 88 branches in the Republic of Ireland as "a kick in the teeth for thousands of loyal customers and staff".
Ged Nash also called for a pause on bank branch closures during the pandemic.
"There is no doubt that Bank of Ireland is exploiting the Covid-19 crisis to drive down its costs," he said.
"The bank's ruthlessly opportunistic plans to cull 88 branches in towns across the State will have an even more severe and direct impact on the fabric of communities across the country than Ulster Bank's recent announcement, given their extensive reach," Mr Nash said.