Prime Minister John Key says he would rather lose power than work with NZ First leader Winston Peters.
His comments came yesterday as he announced that November 26 will be the date of this year's general election.
The poll and the accompanying referendum on MMP will come about five weeks after the end of the Rugby World Cup.
Mr Key said although it could cost National the election, he would not work with Mr Peters. It was up to voters to decide who they wanted in government and he wanted his position to be clear.
"If Winston Peters holds the balance of power it will be a Phil Goff-led Labour government."
The surprise announcement - almost 10 months before the election - is a break from the usual tradition of waiting until the last minute to reveal the date.
Mr Key said although it gave his opponents a lot of time to prepare, he believed certainty was needed early, to allow businesses and the public to concentrate on making the most of the exposure the Rugby World Cup would give New Zealand.
Mr Key had ruled out dealing with NZ First before the 2008 election in the wake of controversy over donations to NZ First.
Little had changed since then, he said.
"In part it's style. As some of you have noted I'm a different politician to a lot of politicians, but I want to lead a positive aspirational government. He's got a very different style and it's rearward looking. I'm about tomorrow - not about yesterday."
Mr Peters himself was quick to retaliate yesterday, claiming Mr Key's decision was "naive, foolish, and sadly arrogant".
Mr Key's stance in 2008 was partly blamed for NZ First's failure to return to Parliament that year. However, yesterday Mr Peters said he expected his support to rally this time.
"New Zealanders don't take kindly to being told what they've got to do, particularly when they're the masters come election day."
Labour leader Phil Goff also believed Mr Key was arrogant for ruling out NZ First prior to voters having their say.
"I'm going to let the voters make the decision."
NZ First party has averaged between two and three per cent support in most recent polls, but last month got 4.5 per cent in a Roy Morgan poll.
Mr Key said the decision did not mean National would ensure its other coalition partners were protected by gifting Act leader Rodney Hide and United Future's Peter Dunne their electorates. He said National would stand candidates in both and would campaign "sensibly".
He said he had no concerns about working with the Maori Party again, despite its MP Hone Harawira openly criticising the arrangement.
He said Act MP Sir Roger Douglas was also critical of National but it had not prevented a constructive relationship with the Act Party. He believed National had shown it could provide a stable government even with support partners from "very different parts of the political spectrum".
Less than two months notice was given for all three elections called by former Prime Minister Helen Clark.
Mr Key would not rule out returning to the traditional teasing out of the date in future.