Ulster Bank are conducting an “urgent” investigation after customers complained about money going missing from their accounts this morning (Tuesday).
Hundreds of complaints from customers in the Republic of Ireland have been lodged, however, the bank claims nobody in Northern Ireland has been affected.
The bank said some customer transactions made since Friday were not showing on accounts.
They are offering those customers emergency cash of 500 euros (£437).
In a statement, a spokesperson for Ulster Bank said: “We are investigating this issue as a matter of urgency and apologise for any inconvenience caused.
“No customer will be left out of pocket as a result of this issue. Emergency cash is available in branch or via telephone.
“Please do not resend the payment as we are working to get these processed as soon as possible.”
In 2012, a computer failure left thousands of customers in Northern Ireland and the Republic of Ireland without funds.