Police say there has been a privacy breach involving more than 100 licenced firearm holders.
In a statement, Superintendant Richard Wilson said an email from the Firearms Safety Authority asking a person to update their address, was accidentally sent to 147 licence holders, revealing their email addresses to each other.
The breach was due to human error, when the licence holders' email addresses were pasted into the 'cc' address field, rather than the 'bcc' or blind carbon copy field, which would have stopped anyone from seeing them, he said.
The breach did not involve information held securely in the authority's systems, and did not come about from any breach of its systems, Wilson said.
Te Tari Pūreke - Firearms Safety Authority said as soon as the problem was identified it sent a follow-up email to ask the 147 recipients to delete the previously sent message.
The authority apologised to those affected and said it would be contacting all those affected on Wednesday afternoon to explain how the breach came about.
Wilson said Te Tari Pūreke had lodged it as a privacy breach and would be notifying the Office of the Privacy Commissioner.
"Te Tari Pūreke has also begun a rapid review of its processes around the sending large batches of email, and will be strengthening its processes to avoid future events like this," he said.