The bank failed to inform customers that their credit card account balances were lower than indicated, slugging them with unexpected fees and interest when they took out cash advances.
The Federal Court on Tuesday found ANZ did not act efficiently, honestly and fairly and was in breach of financial regulations.
More than 186,000 accounts were charged an average of $45 in fees and interest on cash advances between May 2016 to November 2018, with some customers unfairly charged thousands of dollars.
ANZ has since paid back $8.3 million to the affected customers.
The financial regulator said consumers deserved clear and accurate information about their money and what fees they were liable to pay.
“These are errors that we expect a bank to be aware of and fix in a timely manner,” Australian Securities and Investment Commission deputy chair Sarah Court said.
“It should not have taken ANZ several years to address this issue.
“ASIC will continue to take action against banks who fail in their duty to act efficiently, honestly and fairly in dealings with customers”
ANZ also agreed to establish a remediation program to pay back customers who were charged a cash advance fee between November 2018 and September 2021.
In a statement, the bank said the proceedings related to a situation where funds were deposited to a credit card account and displayed as available, and then a cash advance was made on that account before the funds were processed.
It said it accepted responsibility for what had occurred, had apologised to its customers, and had addressed the issues that gave rise to the contraventions.