Published Monday, 02 December 2013
Ulster Bank said it is working to fix the problems. (© PA)
A number of customers took to Twitter earlier to report trouble with online banking, while others said they were having problems with chip and pin.
It comes on what is known as 'Cyber Monday', which is traditionally the busiest day of the year for online shopping.
In a statement the bank apologised for any inconvenience caused to its customers and said it plans to make sure no-one is left out of pocket.
A spokesperson added that some services are now back online.
If customers have been left out of pocket as a result of these system problems, we will put this right.
The bank continued: "We are very sorry for the system issues that affected our customers this evening. Our customers are reporting that services are coming back on line.
"We will confirm when all systems have returned to normal service. If any customer is unable to resolve an issue caused by the disruption, they should get in touch with our call centres or come into a branch in the morning where our staff will be ready to help."
The system problems appear to be UK-wide, with customers at the Royal Bank of Scotland (RBS) Group and NatWest also having their credit and debit cards declined.
© UTV News