According to the bank, people who have been blocked on social media or through other ways of communication have used the reference fields in their bank transfers to send inappropriate messages to others.
BNZ says it is cracking down on this type of behaviour and says it has a message for abusers: "We see you and we'll put a stop to it."
"If you are using bank systems to abuse and harass people, know that we see you and will put a stop to it," BNZ general manager for customer assistance Martin King said.
The bank says it will terminate the accounts of anyone caught using the reference fields to send abusive messages.
"Domestic and economic abuse is unacceptable, and if it's a BNZ customer doing this, you can expect a call from us. If the abuse doesn't stop, we'll end your banking services with us. Simple as that," he says.
According to King, BNZ has spent the past six months analysis its data and building up capability to find people who use their bank transfers to harass people.
"While the number of messages we've found hasn't been large, we are absolutely appalled that this is happening at all," he said.
BNZ has found about 2000 messages per month that it deems "problematic". Most of these include swear words or other abusive terms.
However, King says that is not the full extent of the concerning behaviour.
"Around 20 transactions per month are for very small amounts – a few cents, a couple of dollars. It's clear the amount is irrelevant, what they are doing is using the transaction to send messages to a person," King said.
"The only reason someone would do this is to get around a block or a ban on social media, on messaging applications or SMS. Our analysis shows us these are situations where someone has very clearly said they don't want to hear from another person who's then resorted to using the banking system to get around the block. They do this knowing full well that unlike messaging platforms, bank transactions can't easily be blocked," he added.
BNZ has also found instances of inappropriate messages being sent, alongside larger sums of money.
"In these situations we can see people are using their child support payments to carry out the abuse. This is particularly disgusting as that money cannot and should not be blocked, so the receiver has no choice but to see the abusive messages," King added.
"We're putting a stop to it. Our dedicated domestic and economic abuse banking team will be contacting those receiving these transactions to see what they need and what we can do to help.
"We want our customers to know that they do not have to put up with this. We will listen and work together with them, helping them to set up new bank accounts to escape the abuse, and our specialist team can refer them to support organisations such as Women's Refuges and Good Shepherd NZ," he added.
If you're in danger now:
• Phone the police on 111 or ask neighbours of friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay
Where to go for help or more information:
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
• Shakti: Providing specialist cultural services for African, Asian and middle eastern women and their children. Crisis line 24/7 0800 742 584
• Ministry of Justice: www.justice.govt.nz/family-justice/domestic-violence
• National Network of Stopping Violence: www.nnsvs.org.nz
• White Ribbon: Aiming to eliminate men's violence towards women, focusing this year on sexual violence and the issue of consent. www.whiteribbon.org.nz
