Alongside the new 'Let's do this' campaign battle cry, Jacinda Ardern may have another change in the pipeline - raising taxes.

Labour has promised not to raise taxes in the past, but asked repeatedly today if there would be a policy raising taxes on top income earners, Ms Ardern refused to answer the question.

The potential tax change is a sign of the new power held by the party's finance spokesman Grant Robertson.

Finance Minister Steven Joyce responded: "I know that he [Robertson] likes to tax people more. And he likes to spend more of their money. That's Grant through and through."

In more definitive moves on Friday, Labour's old campaign slogan 'A Fresh Approach' is out and 'Let's do this' is in - Ms Ardern came up with it herself.

"It's come almost inadvertently. When I first wrote a post on social media I finished it with the most natural conclusion; let's do this," she said.

And she won't be sharing any billboards with deputy Kelvin Davis.

"I've got the easiest job in politics, I just need to sit back and bask in the glow of the Jacinda effect," he said.

But the 'Jacinda effect' needs to do more than just glow. It needs grunt and it needs policy.

She has four top policy areas, and will make announcements throughout the campaign focussing on infrastructure, education, housing and the environment.

Ms Ardern has also added some serious backroom firepower to her team, bringing in Mike Munro, Helen Clark's spindoctor and a renowned political mastermind.

He'll take on the role of strategic advisor.

But there was nothing strategic about Kelvin Davis' explanation of the 'Jacinda effect' through his mate "Creature".

"My cousin - his nickname is creature, his real name is Jimmy. We were grave digging. And he goes 'Kelvin I'm voting for Jacinda'... Now...if you can get Creature interesting in voting - she's nailed it," Mr Davis said.

Well, Creature is on board. That's called getting things done.