Winston Peters says he's going to police and the Privacy Commissioner after details of New Zealand First members were leaked to opposition parties and media.
Mr Peters, the NZ First leader and Deputy Prime Minister, took to Twitter saying the leak was malicious misappropriation of data by a disgruntled source, and a serious breach.
RNZ reports a database including the names, occupation, phone numbers and addresses of members and people affiliated with the party has been leaked to news media and opposition MPs.
It reportedly details information as recent as 2016, and includes contact details of Mr Peters and his partner Jan Trotman.
Last week, the party president Lester Gray resigned.