Greenpeace is hoping a court case will help protect the privacy of its staff and volunteers after confirmation they were spied on.
Greenpeace New Zealand's director Dr Russel Norman told Guyon Espiner oil companies are paying private investigators Thompson & Clark "to do their dirty work" and the information is being passed on to the Ministry of Business, Innovation and Employment.
"I think it's totally unacceptable for a government agency to be working with a private investigator like Thompson and Clark while they're following activists to their homes," he said.
"We've lodged the action and the courts will make some decision about the lawfulness of [the surveillance]."
