National's popularity with voters has slipped below 50% for the first time in two years, according to the latest ONE News Colmar Brunton poll.
The poll, taken the week after the Budget, has National's support down four points from November last year to 47%.
Labour and its fledgling leader David Shearer have picked up momentum in the poll, rising from 29% support to 33%.
The Greens have also climbed two points to 13%, while New Zealand First is down one point to just 2%.
Act, the Conservative, Maori and Mana parties all remain steady on 1%.
If the poll is translated into seats in Parliament, assuming all electorate seats are held, National would still have the most, at 58.
Add in a seat each from United Future and Act, and the centre-right would have 60, one short of a majority. That means they would need support, most likely from the Maori Party, to govern.
The centre-left block of the Labour Party, Greens and Mana has edged closer to a majority in this poll with 59 seats.
ONE News political editor Corin Dann says the poll, taken the week following the Budget, will have captured a lot of the backlash to National's education reforms.
"What's interesting about this poll is we've seen plenty of controversies this year for National to have to contend with - the likes of the convention centre, the John Banks saga, Nick Smith - that didn't seem to hurt them in the polls whatsoever. Not this time."
But Dann does not think the result will force the Government to rethink its policies.
"I think National will try and get back on the horse - they know last week was a bit of a disaster public relations-wise - and try and win that argument which they say is about quality teachers over quantity."
Dann said the Greens and Labour would be "pretty happy" with the result.
"A lot of talk about them eating each other's votes. Well they've both gone up in this poll so they'll be pretty chuffed with that."
But Dann said it is not all bad for National. "We're talking a second term Government here, first year in. Forty-seven percent is still historically very high."
John Key remains steady in the preferred Prime Minister stakes with 48% support, the same result as in November.
David Shearer has climbed three points to 14% and is now almost on a par with where Labour's previous leader Phil Goff was during the last election (15%).
The poll surveyed 1005 eligible voters and has a margin of error of 3.1%.