Ulster Bank has apologised over technical problems with its systems.
UTV has been contacted by angry customers who said they have not been able to access their own cash in their accounts on Wednesday.
It is understood some benefit payments have been affected too.
In a statement the bank said it is working to resolve the problem as quickly as possible.
An Ulster Bank spokesperson said: "We are aware of a technical issue affecting a number of Ulster Bank systems which we are working to resolve as quickly as possible.
"We apologise to our customers for any inconvenience this may cause."