Australia's biggest lender Commonwealth Bank will end up paying out as much as $53.1 Million owed to thousands of its workers who didn't get their proper entitlements.

"It is unacceptable that some of our people were not paid the correct entitlements," said CBA chief executive Matt Comyn.  "This should never have happened and I apologise to anyone impacted by these past errors."

The bank discovered the problem during a review in 2017 of superannuation payable to part-time employees working additional hours at single-time rates.  CBA says it is working closely with the Ombudsman and Financial Services Union to correct the problem.  

So far, 41,000 current and former employees have been notified or repaid with $13.2 Million of back pay plus interest.  A further $14.9 million is to follow by the end of next week, and CBA expects to make a further $25 Million in remaining payments by the end of the financial year.