Sustainable NZ launched with high hopes, but that didn't last long.

"We noticed that there was an amount of money missing from the membership," Cartwright told Newshub.

Cartwright quit as party secretary on Monday - a month after uncovering a problem.

In an audit, she realised a number of party members hadn't paid their fees - putting the party's registration in jeopardy.

The lack of financial members "was an innocent mistake," Cartwright told Newshub.

Legally, 500 paid-up members are needed to be an official political party. Cartwright's audit found they were 35 short.

She told party leader Vernon Tava - and says that's when the innocent mistake turned sour.

"His great idea was that we should say we'd collected the money that was missing in cash and that the cash was in a petty cash tin," she told Newshub.

"There was no cash. He suggested he go the bank and get the right amount of cash out."

Cartwright refused.

"Vernon then suggested that we - I - would go into our database which is where we hold all our financial records and doctor the records so the payment received date matched the payment - matched the joining date."

Again she refused. Instead she met with the Electoral Commission without telling Tava.

Newshub has obtained evidence backing up Cartwright's claims.

In a statement, Tava says the party's "acted in full compliance with the Electoral Act".

The Electoral Commission didn't cancel the registration because, Cartwright says, although the submission was incorrect, the party has enough financial members by the time the submission was processed.

But Cartwright says the party's problems go much further. She's one of a number jumping ship, including the party treasurer.

Concerns have been raised by those outgoing members about a lack of policy and funds.

"I don't think they've got a hope of getting to the election as they are which is just so upsetting," Cartwright says.

Tava says assertions about policy and funding are not true.

If you have more information and would like to contact Anna Bracewell-Worrall in confidence, email AnnaBracewellWorrall@mediaworks.co.nz