ACT party leader Rodney Hide is calling for an independent anti-corruption commission to be established to investigate New Zealand First.
Mr Hide has already asked the Serious Fraud Office to investigate donations to New Zealand First and its leader Winston Peters, and has complained to Parliament's Speaker.
However, he says a thorough investigation is needed to get to the bottom of secret funding deals.
"We need an organisation that is independent from government ... actually has the powers to get hold of the various records of New Zealand First and get to the bottom of the money that is has changed hands here."
Rodney Hide says he would like to see a distinguished judge from overseas head an anti-corruption commission.
The ACT Party complained to the Serious Fraud Office after New Zealand First leader Winston Peters refused to answer questions about party donations.
They include $25,000 that businessman Sir Robert Jones says he gave to the Spencer Trust before the last election, which he believed was for New Zealand First.
Last week, New Zealand First leader Winston Peters welcomed a parliamentary inquiry into a donation he received from Owen Glenn.
A complaint about the donation of $100,000 from the Monaco-based businessman to Mr Peters has been referred to Parliament's Privileges Committee by Speaker Margaret Wilson.
Mr Peters initially denied receiving any money from Mr Glenn, but later admitted it went towards the costs of an electoral petition in 2006 after being advised by his lawyer.
He did not declare the donation on a register of pecuniary interests.
Mr Peters says he welcomes the opportunity to set out the facts in the "clear light of day".
Mr Glenn was the Labour Party's largest single donor at the 2005 election.