First Union general secretary Dennis Maga says ANZ staff would have been fired instantly if they were found to have misappropriated company money.
He said there was a double standard for retail staff and the executives at the bank.
Maga points to the example from a few years ago when retail workers took strike action against ANZ because of its low-wage offer. At that time Hisco questioned why he should give a pay rise to those workers "just for waking up early in the morning".
ANZ workers had not forgotten his comments and were outraged to learn Hisco had been enjoying a lavish lifestyle while they were under constant pressure to meet prescribed sales targets.
"You have a CEO that is enjoying bottles of wines and being driven around while these workers are actually facing potential disciplinary action for failing to meet their targets," Maga told the Herald.
"Every time our members commit similar mistakes or others not to that level, the company always uses the term 'trust and confidence' in reference to being an employee of the bank but right now they are changing that narrative - did you have trust and confidence with the CEO?"
Maga said that fact the bank was not requiring Hisco to pay back the "tens of thousands of dollars" did not sit well with its members.
"If ever staff receive an amount of money like an overpayment or unjustified leave or sick leave they have to pay it back. But in this instance, the question is: was he actually authorised to spend and live that kind of lifestyle? If he was not authorised to do so, why wouldn't the company require him to pay it back?"
He said the situation highlighted that ANZ treated its staff and executives differently.
Hisco is believed to be overseas recuperating from health issues which initially saw him take extended leave from the bank at the end of May.
Hisco will leave with his contracted and statutory entitlements to notice and leave entitlements but has had to forfeit about $6 million in equity holdings.