Winston Peters is condemning a "deliberate and malicious" leak of New Zealand First members' personal details to the media.
The Deputy Prime Minister and NZ First leader voiced his outrage over the information being leaked on Twitter. The information included members' names, phone numbers and paid membership statuses.
The details were given to Stuff, which said it included a spreadsheet with an NZ First Auckland database, listing membership details of 799 paying members from as recent as 2016.
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According to Stuff, it showed that fewer than half of those listed were paying NZ First members, with 448 of them due to renew their membership at the time.
Stuff checked the validity of the leaked database and found that it had listed legitimate members, one who said they were surprised and disappointed the information had been stored so carelessly.
"If I had known that it wasn't encrypted then I probably wouldn't have signed up in the first place."
Peters said the information was given to the media by a "disgruntled source", and said despite its age, "this is a serious breach and as such is being reported to the police and the Privacy Commissioner".
Newshub understands NZ First is referring it to the police Wednesday afternoon. A police spokesperson said "any complaint will be assessed".
It follows the resignation of New Zealand First president Lester Gray last week, who told the media he stepped down for "moral" reasons.
It's reported he refused to sign off financial reports after being kept in the dark on the party's spending.
The leaked information also included a proposed NZ First hoarding design that was dismissed by party members because it could be interpreted as racist.
The sign read, "It's about you, not them."
It's a stark contrast to Prime Minister Jacinda Ardern's "they are us" motto, following the March 15 Christchurch terror arrack.