Security company Thompson & Clark Investigations was asked to monitor "issue motivated groups" such as the South Taranaki iwi Ngāti Ruanui.
That's according to a new State Services Commission report commissioned by Energy and Resources Minister Megan Woods.
The security company was given the profiles and newsletters of groups opposing oil and gas exploration and iron-sand mining - and Ngāti Ruanui was one of the main opponents.
"The report says we were monitored and the only other word for that is spying," Te Rūnanga o Ngāti Ruanui CEO/kaiarataki Debbie Ngarewa-Packer said.
The iwi is making an Official Information Act (OIA) request for more information and may make a formal complaint.
It would also like a review of New Zealand Petroleum and Minerals, the government body that manages oil, gas and minerals and issues permits for exploration.
The 150-page report shows "issue motivated groups" such as the Ngāti Ruanui iwi were treated as security threats by several Government departments.
The practice started during Helen Clark's Labour government, with one instance in 2002.
But Ngarewa-Packer said it ramped up during the last National-led government, when Simon Bridges was Energy and Resources Minister.
In 2015 he put up the "largest ever" block offer for oil and gas exploration. New Zealand Petroleum and Minerals was making "a huge effort" to bring business into the country.
Asking for opposing groups to be "monitored" called into question every decision it has made during that period, Ngarewa-Packer said.
"Most iwi in Taranaki would have something to say about how they experienced [New Zealand Petroleum and Minerals] in that particular period."
Ngāti Ruanui has had open relationships with oil and gas companies for 20 years.
"If they had've rung and asked us, we would've told them what we were doing. They're basically monitoring anybody that could get in the way."
The South Taranaki tribe has also opposed iron-sand mining by Trans-Tasman Resources (TTR). During the mining proposal's last hearing process, its people felt their concerns were ignored and officials were biased.
"We feel like were up against not just TTR, but the officials as well."
It seemed paranoid at the time, but Ngarewa-Packer now believes that treatment was part of a prevailing behaviour and culture.