Winston Peters is demanding an apology over a Serious Fraud Office probe into New Zealand First donations ahead of the 2020 general election.
The Court of Appeal on Tuesday dismissed a bid by the SFO to appeal a High Court decision finding two men not guilty of electoral fraud.
The two defendants - who have name suppression - had been accused of obtaining nearly $750,000 by deception between 2015 and 2020.
They were found not guilty in July 2022.
In a statement Peters labelled the case "a malicious attack against a political party going about its lawful business in a lawful manner".
"These were nothing but malicious unfounded attacks by the SFO, Electoral Commission, and especially by some in the media with blatant personal vendettas," said Peters.
"We want an apology."
One of those acquitted told Newshub the failed SFO case proved that the place to determine electoral law is the Electoral Act, and that the failed intent to create a crime under the Crimes Act is repugnant.
The pair were accused of fraudulently depositing money into an NZ First Foundation bank account. Some money was used for NZ First expenses but wasn't recorded as party donations.
Justice Pheroze Jagose ruled the men not guilty as the donations collected weren't handed to the party so didn't meet the definition of a 'party donation' under the Electoral Act.
In its decision, the Court of Appeal panel said the High Court judge had erred by finding the donations were not party donations within the definition of the Electoral Act.
However, the panel found the judge was correct to find the SFO had not proved the men did not believe they had a "possessory right to the donations".
Peters said there was never any evidence or intent to act illegally by New Zealand First or the Foundation.
"The April 2020 attack by the SFO dramatically effected New Zealand First's public image, particularly since the media and political opponents immediately decided that it would not be 'innocent until proven guilty' but the converse - 'guilty until proven innocent'."
The SFO said it welcomed the Court of Appeal decision.
"Today's findings reinforce the importance of both taking the original case, but also appealing the High Court's decision," said SFO director Karen Chang.
"Transparency is key to a well-functioning democracy. New Zealanders have a right to know who is funding our political parties, and this right should not be as easily circumvented as through depositing funds into a trust."
In December 2022, following the High Court ruling, Parliament passed legislation to close the loophole exposed by the case - by clarifying what a 'party donation' is under the law.
"Today's decision confirms that it was always Parliament's intention that such funds would be considered "donations" under our electoral laws," said Chang.
"A robust electoral integrity framework is fundamental for upholding the principles of democracy, protecting citizens' rights, and ensuring the stability and legitimacy of government, as reflected by the recent Independent Electoral Review."
