Bank of Ireland has been fined more than €3.1million by the Central Bank.
The penalty has been imposed for twelve breaches of money laundering and terrorist financing legislation.
The Central Bank says Bank of Ireland failed to promptly report six suspicious transactions to Gardaí.
It also failed to carry out a risk assessment on ways of preventing accounts being used for money laundering.
The Central Bank has described the failures as unacceptable.
Its director of enforcement Derville Rowland said Bank of Ireland fell "far short of the standard expected of one of Ireland's largest retail banks".