Winston Peters has hit out at Labour's tax plans - suggesting a lack of clarity would make any post-election negotiations difficult.

Peters announced a "next generation" SuperGold card at a rally on the North Shore today attended by about 1000 supporters, many of whom were bused in from around the North Island.

Despite Labour's rise under Jacinda Ardern most polls still indicate Peters could hold the balance of power after the election in two weeks' time.

Talking to media after his speech, Peters was asked about who he could go with and said he needed all the facts to make a decision. Asked what those were, he listed some.

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"What is the water tax for the Labour Party? What is the taxation regime going to be for the Labour Party? That is all down to a committee coming.

"We don't know...and particularly those of us engaged in politics. Just two things alone - taxation and water."

Peters was asked if he meant he could not make a call on whether to go into coalition with Labour unless the party revealed what taxes it would introduce.

"It's more by way of illustration of how difficult this is to do. Rather than be pinned down on one of your bottom-lines that don't exist because you don't know what they are...this is one port you are not going to arrive at.

"Did you not get how turgidly boring you people are asking the same question and well before anyone votes. People are voting on Monday all the way until the 23rd. When they have spoken is the first time we will have the most critical tranche of information that we need - what the voters have done.

"Surely in a democracy you understand that. Or should I give you a stint of about five years in North Korea so you might appreciate what I'm talking about."

Labour's tax plans have been a key attack point from National, which says the party is not being upfront about what taxes it could introduce.

Ardern has pledged to set up an expert working group to make recommendations on tax reform, which could include a capital gains tax (excluding the family home).

Previous leader Andrew Little said if a capital gains tax was recommended by the group, he would implement one only after taking that to the electorate at the next election.

Since taking over as leader Ardern has changed that position - saying she will act on recommendations before the next election in order to address the housing crisis.

She has made clear a capital gains tax would not be applied to the family home.

Labour says its price on water would be set after consultation, but it has suggested that it will be around 2c per 1000 litres for irrigators.

In his speech today, Peters also denounced media and economic commentators as "Chardonnay-drinking, pinky finger-pointing know alls".

He told the crowd they were victims of the same discrimination he was subjected to when media questioned when he would retire. Peters cited the example of American businessman and investor Warren Buffett, who is aged 87.

"There has never been so much of an arrogant, age-istic attitude to old people."