Bank of Ireland has confirmed there will be no service for ATM and debit cardholders for several hours.
It says this is due to "scheduled IT maintenance".
There will be no service for ATM and debit cardholders at any ATMs - either Bank of Ireland or non-Bank of Ireland - from 1:00am to 5:00am on Monday May 23rd.
The bank says some ATM/debit card customers may also be unable to conduct point-of-sale transactions.
A similar outage also took place during the hours of 3.00am to 7:00am this morning.
However it adds that credit card point-of-sale transactions will not be affected.
Credit card holders will not have service at Bank of Ireland ATMs - but will have access to services at non-Bank of Ireland machines.
Customers who top up their mobile phone credit using our 365 Online or the mobile and tablet apps will have the credit applied once the service has been restored.
Bank of Ireland ATMs in the Republic, Northern Ireland and UK Post Offices will also be unavailable to any non-customers at that time.