ANZ says it dismissed seven staff who deleted customer email addresses to prevent them giving negative feedback, which may have impacted the employees' incentive payments.
In a statement, the bank said about a year ago it found some staff were manipulating customer records andthose involved were disciplined, with seven losing their jobs.
It said it randomly asked some customers to respond to an email survey about their experiences, but some surveys weren't being sent.
First Union represents frontline bank employees, including 900 ANZ staff.
On Friday Finance Minister Grant Robertson put the hard word on bank bosses during a conference call, telling them he was under pressure to call a royal commission into banking on the back of controversies related to ANZ and its departing chief executive David Hisco.
Robertson said it was not his preference to hold a royal commission, but also indicated that any further revelations of bad behaviour by banks would make the pressure hard to resist.
