Permanent TSB has been fined €2.5 million by the European Central Bank for failing to comply with liquidity rules for euro zone banks.
The breaches occurred over a seven-month period between October 2015 and April 2016.
A penalty of €750,000 was imposed on PTSB after the bank failed to comply with specific liquidity requirements requested by the ECB in February 2015. This breach occurred between 27 October and 31 December 2015.
The lender was hit with a second fine of €1,750,000 for breaching the same rules between 4 January and 26 April 2016.
The ECB said this is the first time a penalty has been imposed on a euro zone bank since the ECB assumed responsibility for the regulation of the area's banks in 2014.
PTSB said the bank had a liquidity buffer of €4 billion at the time of the breaches and its liquidity position was not impacted during the timeframe when the breach happened.
At present, its liquidity buffer is in excess of €6.5 billion.
PTSB said the breaches arose through a "misinterpretation of a revised regulation ... which updated elements within the LCR calculation which related to the treatment of ECB funding. At no point during this period did the Group's actual liquidity position deteriorate".
The ECB said the breaches did not change the liquidity position of PTSB and the bank has since fully rectified the issue.
PTSB said it has cooperated fully with the ECB on the matter.