Greens say real reason is dodging ill will from consumer cost rises.
Prime Minister John Key has claimed a potential clash with the G20 Summit in Australia is behind his decision to set the election two months earlier than usual, but his political rivals say he is going early to avoid a voter backlash from rising power prices and mortgage-rate hikes.
Mr Key yesterday announced September 20 as the election date, saying the possibility of protracted coalition talks and a clash with the G20 summit in mid-November motivated his decision on the date.
He said if the election were held later, it could also jeopardise proposed visits to New Zealand by several world leaders, possibly including US President Barack Obama, around the G20 summit.
However, Green Party co-leader Russel Norman said voter turnout was more important than a G20 summit, and the colder weather in September would detract from that. He said Mr Key was simply attempting to have an election before the impact of mortgage interest-rate hikes and electricity price rises was felt.
"He's trying to go early by getting in ahead of those big impacts on household prices. Democracy trumps all else and the key thing is to maximise the opportunity for New Zealanders to participate, and you [do that] holding it in warmer weather."
Labour leader David Cunliffe said he was happy with the election date and did not expect colder weather to put Labour voters off. "We are ready, we are up for this. It's game on."
Mr Key said potential interest-rate hikes were not a factor in choosing the date. He believed that under MMP, a September date made more sense as a matter of course because it didn't clash with big international summits, such as Apec, and allowed time for a new Government to settle in before the Christmas break.
He also believed NZ First leader Winston Peters should be more transparent about his preferences for a coalition before voters went to the polls. "If NZ First holds the balance of power, goodness knows how long it could take for [Winston Peters] to actually decide what he's going to do."
Mr Peters said he noticed the Prime Minister spent much of his briefing talking about New Zealand First but "he's never talked to us".
Mr Key said he'd make it clear in the weeks before the election if National wanted voters to support another candidate in an electorate such as Epsom.
Mr Cunliffe didn't rule out similar arrangements, but said they weren't on the table at the moment.
Key flags news of referendum
Prime Minister John Key is expected to announce today that a referendum will be held on changing the flag - but Labour leader David Cunliffe has described it as "tokenism" that will distract voters from major issues.
Mr Key announced the election date yesterday, but held off on saying if he intends to hold a referendum on the flag until a speech at Victoria University today.
Although he had previously voiced support for a new flag, he first raised the possibility he would call a referendum on it in January.
He said today's speech would be "thorough and thoughtful" and set out a lot of important points.
Flag options include a two-part referendum, the first to decide whether to change the flag and the second to choose a new design, or giving voters a choice between the current flag and a new design.
Mr Cunliffe said it should be part of a broader constitutional rethink.