Police have been tapping the phones of a New Zealand human rights activist group, in what members say is a massive breach of privacy.

People Against Prisons Aotearoa is a prison abolitionist group which has run campaigns for human rights in prison and against the use of solitary confinement. Three of their members discovered in court documents that their phones have been tapped for an unknown period by the NZ Police.

The phone tap permission was granted on 22 November 2016, after three members of the group occupied and chained themselves to a desk in a Corrections office to protest a trans prisoner being kept in solitary confinement. They faced trespassing charges following the protest, but all three were discharged without conviction yesterday.

A police statement to the court, obtained by VICE, said the phone calls and text messages of those members were continually monitored and recorded, and accessible by the direct investigation staff.

A section of the statement by police on the phone tapping.

Sophie Morgan, 24, is one of the three whose phones were tapped as part of the order. "It's pretty disturbing to know that all this time, the police have been listening in to all kinds of personal conversations. I do really feel violated by that."

"We're not a danger to the New Zealand public at all," she told VICE: the protest action had been non-violent, and was intended to protest the use of solitary confinement on a woman suffering significant mental health issues, she said.

"My immediate response is that this is part of a longer process of police quite clearly trying to undermine our capacity to organise and do the work that we do. It's an absolute breach of privacy and very concerning," she said.

She said the tapping of phones threatened freedom of speech and the right to organise and protest. "Everyone in New Zealand should be worried about that, whether they're part of the protest community or not."

Morgan says the three still don't know the extent of the tapping, or whether their phone calls and messages could still be accessed by the New Zealand police. The statement does not give an end date for the tapping.

Last year New Zealand Police were granted 110 surveillance device warrants, according to their 2015/16 Report. Of those, 95 granted use of an interception device, 93 granted use of a tracking device, and 63 granted use of visual surveillance devices.

On 44 occasions, the police also used surveillance or interception devices without a warrant.

Police can conduct warrantless surveillance under changes to the Surveillance Act made in 2012. Assistant Police commissioner Malcolm Burgess said at the time that while police could complete some forms of surveillance and searches without warrants, the situations were 'common sense'.

"Either emergencies, where life might be at risk, or where the destruction of evidence might occur in very serious circumstances,'' he said.

People Against Prisons Aotearoa spokesperson Emilie Rākete told VICE the tap was "a blatant breach of the basic human right to privacy. People with political beliefs inconvenient to the government deserve this right as much as everyone else."

"It demonstrates the lengths to which the police are willing to go to undermine our organisation. This is a politically motivated attack by the New Zealand Police."