Commonwealth Bank customers facing bill fees caused by the bank's network outage aren't guaranteed refunds.
But the bank says while its focus is on restoring services to full operation it's also open to "discussing" late fees with those who've incurred them.
Digital retail banking boss Pete Steel on Tuesday apologised to millions of customers for the issues on Monday which he admitted was a "tough day".
Many customers were unable to log into the CommBank mobile app and NetBank system throughout Monday or experienced delays.
"Our teams have worked very hard during the night and I am pleased to say we've restored all services and we can reassure customers that everything will be working today as they expect," he said in a statement.
The issue also affected bill payments and transfers, with outstanding requests set to be processed by close of business on Tuesday.
The CBA's social media team encouraged those facing late payment fees to contact them.
"We wouldn't want you incurring fees as a direct consequence of the outage," it posted several times.
A problem in one of the two data centres supporting the NetBank system was blamed for the problem. The root cause of the issue will be "fully investigated", a CBA spokesman said.
The increased demand on the one, unaffected data centre led to some customers being unable to login at all and extended delays for others.
Meanwhile, those using Visa cards issued by other banks were unable on Monday to make payments at businesses using CBA EFTPOS terminals.
Commonwealth Bank boasted more than 16 million customers in June this year - though this was down half a million on the previous year. Digital customers increased five per cent to 6.5 million.
Australian Associated Press
