Ardern is still the preferred Prime Minister at 45.5 per cent, down 2.6 points. National leader Judith Collins has jumped by the same margin up to 8.2 per cent, but sits behind Act leader David Seymour on 8.6 per cent after he received a 3 point bump.
When asked who they preferred, voters chose Seymour over Collins by a significant margin - 41.7 per cent to 25.9 per cent, with 32.4 per cent reporting they did not know.
The Labour-led Government has come under increasing scrutiny over the Covid-19 response since the last Newshub-Reid Research poll in May, in particular the vaccination rollout and immigration and managed isolation and quarantine issues.
It has also faced strong public opinion on reforms announced recently, nurses' pay and conditions, and the clean car feebate with proposed fees for new utes to discount electric vehicles.
The latter was part of a protest from farmers across the country.
The poll also follows a turbid few months for the National Party, with the high-profile retirement of veteran MP Nick Smith citing an employment issue, and former leader Todd Muller's forced retirement.
The poll results showed while support for Labour had slipped, it was not moving where it traditionally might have, and instead Act continues to build support.
Results from the last Newshub poll in May showed Labour at 52.7 per cent (up 2.7 percentage points from election night), and National at 27 per cent (up 1.4 points).
In the preferred PM stakes, Jacinda Ardern polled at 48.1 per cent (down 4.5 points); Judith Collins was at 5.6 per cent (down 12.8 points).
Former prime minister John Key was higher than Collins on 6.7 per cent, while backbench MP Christopher Luxon was on 2.4 per cent.
Tonight's Newshub-Reid Research poll has a margin of error of 3.3 per cent and was conducted over July 22 to July 29.
