The Ulster Bank apologised but said no one was left out of pocket after its online services were hit by problems on Friday morning.
"We're still working through what the issue is there".
RBS blamed a "technical issue" for rendering their online services unavailable to customers for approximately four hours before systems were fully restored just after 10am.
A statement from RBS said: "We would like to apologise to customers who experienced issues logging into their online and mobile banking accounts this morning, this issue has now been resolved".More news: Cyclops Firmino sets new Champions League record
It comes after City A.M. yesterday reported that Barclays faces a Treasury Select Committee investigation into a failure that saw customers unable to use its online banking services for six hours earlier this week.
"We are aware that customers are now experiencing issue logging into their online and mobile banking accounts", a spokesperson told IT Pro this morning.
Combined, the three brands have about eight million online and mobile customers.
"We're aware of some issues on our Online and Mobile Banking services and are working hard to fix them".More news: Google Still Lets Third-Party Devs Scan Your Email
He added that: "Customers can still use ATMs and telephone banking or visit their local branch". "The team are working very hard to get it back up for customers".
The glitch came a day after some Barclays customers were left struggling to log into accounts due to a technical problem. Not really acceptable for our 24 economy!
Emma Foley said: "I need to transfer money over to pay my bills are you going to pay my late payment charge?"
Earlier this month, RBS announced plans to swing the axe on another 54 branches, 14 of which are the last bank in town - meaning there are no other bank or building society branches in those areas.More news: Arrested Demonstrating Support For Christine Blasey Ford