The Conservative Party says it is miffed about being kicked off the line-up for the first political debate of election year.

But the party won't follow in the footsteps of its former leader Colin Craig and take the issue to court, new leader Leighton Baker says.

The University of Auckland Debating Society is hosting the debate on Thursday, and representatives from National, Labour, Greens, New Zealand First, the Maori Party, United Future and Mana will take part.

The Conservative Party was originally invited in November, but the invitation was withdrawn on Friday.

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The society's president Callum Lo said the organisation did not expect so many parties to respond, and it had decided to limit participatation to parties which were in, or had been, in Parliament.

That meant there was no room for the Conservatives or The Opportunities Party.

"The lineup had become quite bloated," Lo said. "We had 11 or 12 people and for an hour and a half debate we were looking at only around eight minutes per person."

Baker said his party's exclusion was "a wee bit unjust" given the Conservatives had polled fifth-highest in the last election, and higher than four other parties being represented at the debate.

It was also "common courtesy" to uphold an invitation, he said.

In 2014, Craig successfully challenged TV3 in court after being left out of its minor parties debate.

Baker said he wouldn't go that far on this occasion: "That's not how we roll".

The Conservatives received 3.97 per cent of the vote in 2014 but failed to get into Parliament because they fell below the 5 per cent party vote threshold and won no electorate seats.

The party has since been torn apart by the departure of founder, leader, and main funder Colin Craig amid allegations of "inappropriate conduct" in relation to his former press secretary in 2015. It did not register in a One News Colmar-Brunton poll last month.

Baker said he was determined to prove the Conservatives were not a one-man party and they were busy working on policy and recruiting candidates for the election.

He said the election campaign would be "much more grassroots" without the financial backing of Craig, a millionaire property manager who funded most of the party's campaign.