New Zealand First leader Winston Peters is calling for the party to make a police complaint over a "massive breach" of party information.

"This morning I have recommended to the New Zealand First Party president that she begin preparing a complaint to the police over the massive breach of party information," Peters said.

"Ongoing media stories using as their source stolen information are designed to skew an even political playing field.

"New Zealand First has so far been sensitive to the circumstances surrounding the theft of party information but can no longer tolerate the mendacious attacks against the party and its supporters."

The breach referred to by Peters is thought to be related to a series of news reports about the New Zealand First Foundation, a vehicle which receives donations, and which pays for many New Zealand First party expenses.

The Electoral Commission is looking into the foundation in the wake of the news reports to decide whether it has been used lawfully.

It could refer the matter to the police if it has concerns.

The most recent report, by RNZ last week, detailed donations to the New Zealand First Foundation, which do not need to be declared if they are under $15,000. It did not allege that the donors had done anything wrong but questioned whether the party needed to have disclosed them.

RNZ's Guyon Espiner had very detailed accounts of donations. For example he reported that last year companies owned by Graeme Hart, New Zealand's richest man, donated nearly $30,000 to the New Zealand First Foundation in two amounts that each fell just short of the $15,000.01 level at which political donations must be publicly disclosed by the party.

He said RNZ had seen documents showing that Church Bay Farm, which is 100 per cent owned by Hart, donated $14,995 to the New Zealand First Foundation on 29 March, 2019.
On the same day Walter & Wild, two thirds owned by Hart, also donated $14,995 to the New Zealand First Foundation.