Greenpeace wants the police's own inquiry into external security consultants to be more independent.
The environmental group claims police used controversial group Thompson and Clark to spy on its activists.
But an official State Services Commission (SSC) inquiry into security practises does not include police.
Greenpeace executive director Russel Norman says there can't be any bias.
"There's no particular reason the police can't invite the SSC investigators in to oversee an inquiry inside the police."
The police instead are doing their own inquiry.
"We recognise public concerns about the use of such consultants by state sector agencies," Police Commissioner Mike Bush said on Friday.
"Our vision is to have the trust and confidence of all and it is appropriate that police actions in this regard are closely considered to ensure we meet the expectations of the public."
Dr Norman, who claims he was spied on, says there needs to be independence.
"If the police have been using Thompson and Clark to place paid informants inside groups that are opposing Government polices… that is a fundamental problem to our democracy."
Prime Minister Jacinda Ardern ordered Govenrment departments to stop using Thompson and Clark earlier this year, after Newshub revealed the firm was being used by Government insurance company Southern Response to spy on Christchurch earthquake victims.
- Patrick Gower: Why the Thompson & Clark investigation matters
- $180k of taxpayer money used to spy on Kiwis after Christchurch earthquakes
- PM Jacinda Ardern bans private investigators behind Southern Response spying
The police weren't included in that directive.
"The police have it entirely within their powers under the current rules to invite the State Services Commission investigators in to run the inquiry inside the police and to directly cooperate with the SSC investigators," said Dr Norman.
Newshub.
