AIB has apologised for an error in its reporting of missed loan repayments to the Irish Credit Bureau (ICB).
The Office of the Data Protection Commissioner has said AIB's misreporting to the ICB amounted to a serious breach of data protection law, at the upper end of the scale.
The error, which happened over a six-year period up to July 2012, was identified in May this year and reported to the Data Protection Commissioner by the bank.
Deputy Commissioner Gary Davis told RTÉ News that AIB supplied inaccurate personal data to the ICB. That is a breach of data protection law, whose effect may have been the refusal of loans.
AIB has admitted that incorrect information on around 12,000 of its customers was sent to the Irish Credit Bureau over six years up to last month.
The data involved was part of a mass of information collected by the ICB about the loan repayment track records of millions of borrowers.
It is used by banks as a key factor in deciding whether or not to lend to customers.
In a statement, AIB said the error related to certain customers who were in arrears on loans to the bank.
AIB has apologised and written to the those affected. It also said customers could contact the bank at the helpline number in the letters and has offered to request a new copy of any affected customer’s ICB statement at AIB's expense.
The Irish Credit Bureau has said it has fully corrected all relevant customer records. Mr Davis urged every affected customer to get a copy of their credit report to check its accuracy.