Ulster Bank is to sell 5,200 non-performing mortgages to so-called vulture fund Cerberus.
The portfolio of loans, valued at €1.4bn, includes around 2,300 mortgages relating to private homes and around 2,900 mortgages covering buy-to-let properties.
However Ulster Bank said that no performing loans were included in the portfolio, while none of the home loans involved were in a restructuring arrangement with the bank.
Some of the portfolio's buy-to-let loans may be in an arrangement with the bank, however it said that none of the loans included were considered to be sustainable.
Ulster Bank also said that a mortgage holder's rights transfer with them as part of the sale, and must be respected by the acquirer.
Affected customers will now be contacted by the bank and given 90 days notice of the sale.
Ulster Bank has also established a helpline - which customers can reach at 1800 435 763.
Of the portfolio's €1.4 billion around €740m is relating to buy-to-let mortgages.
Ulster Bank says these mortgages have been, on average, in arrears for 34 months and have average arrears of €32,000.
Meanwhile there are around €615m worth of private dwelling home loans in the portfolio. These have been arrears for an average of 83 months, with average arrears of €61,000.
On average, these mortgage holders were involved in three restructuring arrangements with the bank in the past.
The bank said that following the sale the percentage of non-performing loans on its loan book would fall from around 17% to under 12%.
David Hall, CEO of the Irish Mortgage Holders Organisation, said the figures highlighted the fact that many simply cannot afford to repay their mortgages.
"Ulster Bank say that of the 2,300 family homes they are selling to vultures the family have been in an average of three mortgage restructuring arrangements," he said. "This proves the point which banks and their mouthpieces are ignoring. It’s about people's ability to pay, not their willingness.
"Anybody who has engaged with their lender and provided documentation to attempt to restructure their homes an average of three times cannot be accused of not engaging or strategic defaulting."
Fianna Fáil's finance spokesperson Michael McGrath criticised what he described as the "outsourcing" of enforcement activity.
"While it is certainly the case many of these mortgages have been deep in arrears for some time, the net effect of the transaction remains that another bank is outsourcing its dirty work to a US vulture fund," he said.
"What tools does Cerberus have at its disposal for dealing with these loans that Ulster Bank doesn't have? The bottom line here is the banks and the government are simply washing their hands of the problem."
However Ross Maguire of New Beginnings said that vulture funds are often more willing to engage with customers than banks and can be more "creative" in the solutions they propose.
This can include debt write-downs, which he said Irish banks are not willing to consider.
"Funds are much easier to do a deal with than the banks," he said. "They are keen to do a deal."