New Zealand's main journalists' union is demanding Deputy Prime Minister Winston Peters apologises to the reporters he initially claimed his party had taken secret photos of.

E tū, the country's largest private-sector union, said Peters – also NZ First Leader – needed to provide "categorical assurances" that nothing like this would happen again.

Peters initially admitted to having photos taken of two reporters investigating the mysterious NZ First Foundation.

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But in a tweet last night, he walked back his comments to Magic Talk that "we took the photos", saying that they were actually taken by NZ First supporters.

E tū senior national industrial officer Paul Tolich was not to convinced by Peters' comments.

"Peters needs to apologise to the journalists," he said in a statement.

He is seeking assurances from New Zealand First that the party is not involved in tracking journalists as they go about their work.

"Mr Peters and his party might be unhappy with the reporting of the party's fundraising, but journalism's role is to hold those in power to account without fear or favour," Tolich said.

He said these sort of tactics were "chillingly similar" to other examples of attacks on journalists in countries where the freedom of journalists is suppressed.

Although Peters has a testy relationship with the media, he has also fought for the fourth estate as well.

"My party's fundamental position always has been and remains that a fourth estate is essential," he said in December when throwing his support behind an NZME and Stuff merger.


He did, however, go on to berate press gallery reporters for being too young during the very same media conference.

Tolich is not the only one calling on Peters to back off.

National deputy leader Paula Bennett this morning called on Prime Minister Jacinda Ardern to pull Peters into line.

"I think if there is more to this, it's really leading to her having to [explore] some pretty serious consequences.

"She is the Prime Minister, this is her Deputy Prime Minister, she has to step in and tell us what kind of politics she will accept."