Activists opposed to the Waihopai spy base near Blenheim have clashed with police as they tried to gain access to the complex.
The Christchurch-based Anti-Bases Campaign held its annual protest rally at the base today, where there was a significant police presence.
Members of the protest group climbed a fence but were forced back by police.
However, they said they were attempting to deliver a letter to the base commander asking for clarity over who it actually spies on.
They said they were concerned by the activities carried out at the base, following revelations that a Government agency illegaly spied on internet tycoon Kim Dotcom.
Spokesman and organiser, Murray Horton, said he will continue to put pressure on the agency until it comes clean about its activities.
Horton claims the work conducted by Waihopai spy base is illegal, and his group will not "stand by and let them get away with it".
He also wants the base to be closed and the building dismantled.
"[Waihopai] is an American spy base operated by New Zealanders and paid for by New Zealanders but working for agencies like the National Security Agency. It's an outpost of US intelligence," he is reported as saying.
"It compromises New Zealand independence, our sovereignty, and our anti-nuclear policy. It's also an enormous waste of money."
The group has picketed the base almost every year since its construction was announced in 1987.
During a 2008 protest, three activists managed to deflate the spy base's protective dome.
- with Newstalk ZB