The New Zealand Government should denounce the arrest of whaling protester Pete Bethune and use all available diplomatic channels to bring him home, the Green Party said today.

"The brutal practice of whaling itself that should be on trial, not people like Pete Bethune who are trying to prevent it," Green Party Oceans Spokesperson Gareth Hughes said.

New Zealand citizen Pete Bethune of the Sea Shepherd Conservation Society, is on trial in Japan for trespassing on a Japanese whaling vessel while staging a non-violent protest.

"John Key's Government has refused to denounce Mr Bethune's arrest, and is leaving him to negotiate the Japanese legal system himself.

"The Government should be using all diplomatic channels available to bring Mr Bethune home," Mr Hughes said.

The Greens will move a notice of motion in Parliament today calling on all parties to support the use of diplomatic channels to secure Mr Bethune's return to New Zealand. They will also ask for an urgent debate on the subject.

Mr Hughes will also ask Foreign Minister Murray McCully directly if he will call on the Japanese Government to release Mr Bethune. It will be Mr Hughes' first oral question in Parliament since becoming an MP a month ago.

"New Zealanders have an honourable tradition of non violent direct action. In acting against the Japanese whalers, Mr Bethune was defending a view most New Zealanders share," Mr Hughes said.

"The Government's refusal to support Mr Bethune raises serious questions about New Zealand's attitude towards its citizens stuck in the legal system of other countries where jurisdiction is highly dubious.

"We are concerned that Mr Bethune will not have a fair trial in Japan. The Japanese media have labelled him a terrorist, and Japan has a poor track record of responding fairly to criticism of their illegal commercial whaling.

"It is the Japanese whalers who should be going to court for their illegal commercial whaling - thinly disguised as scientific research - in the Southern Ocean Sanctuary.

"Instead of 'compromising' to allow commercial whaling at the next Whaling Commission meeting in June, New Zealand should join Australia and prepare a case against Japan for the International Court of Justice," Mr Hughes said.