Gareth Morgan has accused the Act Party of gunning for his political party by making petty complaints about its election campaign and party rules.
Morgan's The Opportunities Party was cleared by the Electoral Commission today of "treating" in the Mt Albert by-election.
Act Party leader David Seymour laid a complaint with the commission after The Opportunities Party's Mt Albert candidate Geoff Simmons offered free shuttle services to Mt Albert residents over the weekend.
The commission said today the shuttle service did not qualify as treating - offering people money or goods in exchange for their vote - and said it would take no further action.
Seymour said he was shocked about the commission's ruling.
"If you can offer a service with your party livery all over it exclusively to electors of an electorate in the middle of a by-election, then they have made the law meaningless."
Morgan said it was the second time Act had taken action against his party, following an earlier complaint about its constitution.
"It is pretty yucky stuff that he's accused us of. They're clearly severely threatened by us."
In a column in November, former Act Party leader Rodney Hide said Morgan's party constitution was undemocratic and he would be surprised if the party was registered by the Electoral Commission. Seymour said he was not aware of any formal complaint laid by his party on the issue.
He rejected Morgan's criticism, saying The Opportunities Party was not a threat to Act because it was "fishing in a different pond".
"They want to tax people's houses. Nobody who is thinking of voting for Act will be interested in that."
Simmons is running against Labour's Jacinda Ardern, Green Party MP Julie Anne Genter and 10 other candidates in Mt Albert.
The Opportunities Party is using the by-election as a "dry run for the big event", Morgan said.
Next week, the party will start the recruitment process for general election candidates. Morgan said he had been approached by former MPs and candidates but was not interested in them because they did not fit with an anti-establishment party.
It is campaigning for the party vote and wants to get at least five or six candidates into Parliament. Morgan reiterated that he will consider withdrawing the party if it is not polling well close to the election.
The Opportunities Party has announced five policy packages so far, including a pollution tax for farmers, a tax on equity including houses, free pre-schooling, and the creation of an Upper House in Parliament.
All of the policies would be fiscally neutral, Morgan said.
Unusually high advance voting in the Mt Albert by-election has been put down to a calculation error.
On Friday, the Electoral Commission reported that nearly 2000 people had voted in the first four days since advance voting opened.
That was more than double the rate of advance votes over the same period in the general election - a surprising trend given by-elections usually have much lower turnouts.
On Monday, the figures were altered to say fewer than 800 had voted in total.
A spokeswoman said a calculation error "meant that daily totals were accumulated rather than day-to-day". The commission has apologised and corrected the figures.
Nearly 2300 people have now cast votes over eight days - around 500 votes fewer than during the general election.
Voting closes on Saturday.