The National Party's support is faltering in the wake of a series of political difficulties this year.
Support for National slipped to 45.8% in the latest 3 News/Reid Research poll, taken after the Government hit trouble over its plan to increase class sizes.
National received 47.3% of the party vote at the general election last November and in the previous 3 News poll in April scored nearly 50% support.
National also dropped in the One News Colmar Brunton poll earlier this month, the New Zealand Herald poll last month and a series of Roy Morgan polls in the past four weeks.
Support for the Labour Party rose to 33.2% in the 3 News poll, its best result in this survey in two years.
The Green Party recorded 14.4% support, while other parties scored well below the 5% party vote threshold, with New Zealand First the highest on 2.8%.
The poll of 1000 voters was conducted from 29 May to 6 June, and has a margin of error of plus or minus 3.1%.