Bank of Ireland has been fined €3.15m by the Central Bank for breaching rules which prevent money laundering and financing of terrorists.
Bank of Ireland admitted the failures and said the fine related to breaches of controls, as opposed to actual money laundering or financing of terrorists.
It is the fifth significant fine imposed on a financial institution by the Central Bank under new powers.
The Central Bank said Bank of Ireland failed to quickly submit six suspicious transactions to gardaí and the Revenue Commissioners. It also failed to assess the risks adequately.
Meanwhile, Bank of Ireland neglected to ensure banks with which it was doing business with outside of the EU complied with rules.
The Central Bank said financial institutions were required to monitor systems to combat money laundering and financing of terrorism.
It said the high volume of breaches in Bank of Ireland's case pointed to significant weaknesses.
Derville Rowland, Director of Enforcement with the Central Bank, said: "Reporting suspicious transactions to the authorities without delay is a fundamental component of an anti money laundering and counter financing framework."
She added the behaviour by Bank of Ireland was unacceptable and fell far short of the standard expected of one of Ireland's largest retails banks.
Bank of Ireland said it took its responsibilities seriously and had fully co-operated with the investigation.