About 100 protesters marched to the gates of Mt Eden Prison, in Auckland, on Saturday afternoon to demand the release of Tame Iti and Te Rangikaiwhiria Kemara.
The two men were this week sentenced to two years and six months for illegal possession of firearms and restricted weapons at military style camps, in Te Urewera National Park.
The protesters banged on the prison fences. Supporters told the crowd the prison sentences are racist and that Iti and Kemara are political prisoners who must be freed.
The protest on Saturday was one of several that have taken place and more are planned Rotorua, Palmerston North, Dunedin and Christchurch around the country in the coming days.
Iti's son, Waireri Iti, says people are coming out to protest because they sense injustice.
"It's because people are unhappy with the sentence that Dad's got, and the way the whole thing has been handled."
Mana Party president Annette Sykes people are compelled to protest when they see an injustice.
Iti and Kemara's co-accused, Urs Signer and Emily Bailey, were on Thursday sentenced informally to nine months, but the judge adjourned their case to assess whether that term can be served at home.
In his sentencing, Justice Hansen said the group was establishing a private militia and had serious intent. Police Commissioner Peter Marshall said this validated the investigation and raids.
But Iti's lawyer Russel Fairbrother said Mr Marshall is seeking vindication on tenuous grounds.