The Greens says court action is the only way to end the Japanese whaling programme, now that the diplomatic process has failed.
The International Whaling Commission meeting in Morocco has given up its attempts to break a 24-year deadlock between whaling nations and their opponents.
Last month, Australia filed a case with the International Court of Justice, alleging that Japan has breached the whaling convention by continuing to hunt in the Southern Whale Sanctuary.
The Green Party's oceans spokesperson, Gareth Hughes, says it's time New Zealand joined Australia's court action.
Mr Hughes says that in Japan there is an oversupply of whalemeat and falling demand, and that a court injunction could end its programme altogether.