While the Electoral Commission is looking into the allegations, it has limited powers, and there are calls for Prime Minister Jacinda Ardern to involve police in an investigation.
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NZ First leader and Deputy Prime Minister Winston Peters said in a statement yesterday he was "confident that New Zealand First has operated within electoral laws, now and for the last 27 years".
"Declarable donations were declared to the Electoral Commission.
"Our system of democracy is based on the secrecy of the ballot and privacy of party memberships and donations within specified limits.
"We look forward to discussing this matter with the Electoral Commission."
National leader Simon Bridges told Newstalk ZB's Kate Hawkesby this morning the saga went to the heart of the Government's integrity.
While Ardern could stand down NZ First leader Winston Peters, who is Deputy Prime Minister, that would not let her "wash her hands" of the matter, Bridges said.
"What we need is a full independent investigation," he said.
"It's a pretty simple situation - she's talked about the spirit of the law. This isn't the spirit of the law, it's the black letter of the law."
There has been speculation Ardern could call for a snap election. Bridges said National would welcome that but it was unlikely.
"Turkeys don't vote for an early Christmas."
Bridges still wouldn't rule out working with NZ First after the election - saying it was "premature" to do so before an investigation was complete.
"It hardly makes it more likely that we're going to go with NZ First...there's smoke, if the facts are made out there's fire here."