The bankers' union, Finsec, says the ANZ bank should have consulted with its customers over a major review of its branch network.
The bank announced plans for the review and called for voluntary redundancies.
Finsec staff conducted an informal questionnaire of 332 ANZ customers leaving branches in Auckland, Hamilton, Wellington and Dunedin over three days last week.
Of those questioned 93% said they didn't support a reduction in frontline staff in ANZ branches, and 96% said branch staffing cuts would have a negative impact on customer service.
Finsec's Campaigns Director, Andrew Campbell, says ANZ has said it will not be consulting customers during the branch review process.
He says the bank should reconsider that position, as customers have expressed very strong concerns about the impact of staff reductions.
ANZ was unavailable for comment.