NZ First leader Winston Peters says there's only four parties in the mix leading into the election and all of them should get a fair go in all leader debates.

Winston Peters wants a fair go leading into the election and says it would be "anti-democratic" for any media to host leader debates without NZ First.

Peters, the anti-establishment politician, says not having his party represented in election campaign debates would be "blind political prejudice" or the media "deliberately" trying to protect National and Labour - the "establishment parties".

He said in the past state-funded broadcasters, Radio New Zealand and TVNZ, had been "dominated" by National and Labour not to include other parties and had so far got away with it.

"In an MMP environment having leaders of only two political parties represented in a debate provides a skewed view." - Greens co-leader James Shaw

"In the UK there's no way (David) Cameron would have got away with that. He didn't get away with it and he was forced to debate the leading contenders."

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Peters said at this point there were only four parties in the mix - National, Labour, NZ First and the Greens - but "most profoundly in terms of a leader's debate, ruling out NZ First would be blind political prejudice".

"I'm calling it out right now. What we want is a fair go to talk to the New Zealand public and we're entitled to it."

Greens co-leader James Shaw is backing Peters and said his party had been advocating for leaders of multiple parties to be included in all debates for several decades.

"In an MMP environment having leaders of only two political parties represented in a debate provides a skewed view."

While drawing the line on how many political leaders should take part is difficult, Shaw said a "reasonable place" would be to include the four parties that poll above the five per cent threshold.

National Party campaign chair Steven Joyce says it's a long-standing policy for the leader to participate in a number of one-on-one debates between the Prime Minister and the "alternative candidate for Prime Minister".

That position is held by the leader of the largest opposition party, which is "currently Mr Little," Joyce said.

Leader debates have caused controversy in the past - in 2005 two political leaders took their exclusion from a TV debate all the way to the High Court and won.

United Future leader Peter Dunne and then-Progressives' leader Jim Anderton took exception to not being invited to take part in a TV3 televised debate and the court ruled in their favour.

TV3 was forced to include the pair in the debate and it sparked a flurry of other minor parties, Alliance, Destiny and Christian Heritage, to also demand they be included in future debates.

In the end all eight parliamentary parties were represented instead of the six the channel had wanted.

Peters has long discounted media polling.

He said in the 2014 election the polls were "dramatically out and underestimating where NZ First was going to be in the end".

"They would have had us at something like three per cent at this point last time round. Now we know polls are well into the teens and we haven't in anyway brought this campaign to the height of possibilities for us," he said.

Labour leader Andrew Little has been contacted for comment about the leader debates.