A human rights lawyer says the New Zealand police force is showing signs of acting like an authoritarian, "Big Brother" republic.
The Sunday Star Times reports police officers from the Special Investigation Group have carried out surveillance on protest and community groups like Greenpeace.
Police informer Rob Gilchrist has told the Sunday Star Times he carried out surveillance while being a key member of several groups over the past decade, including Safe Animals from Exploitation (Safe), Peace Action Wellington, GE-free groups, and Save Happy Valley, an environmentalist coalition seeking to prevent high-impact West Coast mining that could threaten several species in the area, including the Powelliphanta snail.
But lawyer Michael Bott says it is bizarre police investigators would bother with people trying to save snails.
He says, for example, that political parties have run foul of the Electoral Finance Act, and by analogy he asked if it would justify the police putting a plant into the Labour and National parties.
Nicky Hager and Anthony Hubbard reported in the SST that officers went as far as forming intimate relationships with group members, sometimes having a presence in animal rights or poverty action groups that lasted for months or years. They claim that police sought information on members' personal lives, rather than their activist work alone.
Police say they will neither confirm nor deny the existence or identity of informants, while Phil Goff, leader of the opposition, is asking why police felt compelled to spy on an established and widely-respected NGO like Greenpeace. The SIG was formed in 2005, during the last Labour government - it was claimed that such a group was needed as a domestic response to the September 11 terror attacks.
However, Bott says this type of thing happened in Soviet Russia under the reign of Joseph Stalin, and is concerning this type of informer surveillance could have happened in a liberal democracy.
He believes the matter needs to be independently investigated.
A Christchurch woman who learnt Gilchrist, her partner of eight years, had been spying on her for the police says she is still shocked and devastated.
Rochelle Rees says she met Gilchrist at an animal rights meeting and their relationship was based on what she thought were common values and goals. She says she was disgusted to learn he was not the man he had claimed to be, but is even more disgusted at the way police used him.
Rees says the SIG needs to be prevented from investigating unnecessary groups.
Meanwhile, Green MP Keith Locke is calling for an inquiry, decrying police's "Stasi tactics".
Locke reiterated that technically illegal protests and non-violent civil disobedience did not justify trying to undermine and infiltrate groups that were the country's social concience.
The Greens say they will raise the matter with Police Minister Judith Collins in the coming week.
While Collins has not expressly defended the actions of the SIG, she told the Sunday Star-Times that from time to time police may find it necessary to use paid informants, and said New Zealanders should feel reassured that police were out keeping a watch on the whole community.