The ANZ Bank will cut up to 800 jobs before the end of the year following an announcement to staff.
The announcement was made in Melbourne by ANZ chief executive Mike Smith on Friday, ABC reports.
The cuts will take place over the next few weeks.
The Finance Sector Union said the bank was using the financial crisis as a cover for the cuts.
"The ANZ are providing no explanation as to why the job cuts have got to get bigger," National Secretary of the Finance Sector Union (FSU) Leon Carter told ABC.
"They continue to be a very profitable organisation, they continue to enjoy the benefits of all the stuff the federal government is putting in place.
"This is simply about using the financial crisis as cover to get people to lose their jobs, save costs and maximise money for shareholders."
He said ANZ workers and customers would suffer the most from the move.
The cuts are likely to come from the bank's middle management while branch and call centre jobs are expected to be safe.
In November the FSU said as many as 3,000 jobs at ANZ could go before Christmas.
