Bank of Ireland has said a "technical error" is to blame for incorrect information about their customers being posted on the Central Credit Register.
The register - which documents a person's credit history - is consulted by lenders when considering a loan application.
The Central Credit Register (CCR) was established in the past year to replace the Irish Credit Bureau.
The register logs all loans exceeding €500 in value and ensures lenders can access customer’s credit history through a central database while they are deciding whether to grant a loan.
Up to 3,000 BOI customers had their information wrongly recorded between November and January and the bank corrected the mistake in early January.
It means customers may have been refused a loan because their record held false data about them.
Brendan Burgess from Ask About Money has this advice if you're thinking about applying for a loan.
Mr Burgess said: "Anybody who is taking out a loan in the future, like a mortgage in six months or a year's time, you should get onto the Central Credit Register.
"It doesn't cost anything to look at your record just to see what's on it in case a mistake has been made by Bank of Ireland or by any bank. You can go online and you can register quite easily and you can get a copy of your report."
He said there is an easy way to find out if you have been affected by the mistake.
“If you applied for a loan and you were rejected – and you were sort of surprised that you were rejected – get on to the Central Credit Register,” he said.
He also outlined the impact the error may have had.
He said: "1,500 people had a loan and those loans were put down on 1,500 other people’s records.
“So there are people who might have got loans because the bank didn’t realise they had loans elsewhere.
“Then, of course, there are people who might have been refused loans because they had extra loans on their accounts.”