New Zealand has rejected Japan's claim to be legally whaling in the Antarctic as an attempt to reduce the global whaling treaty to an industry cartel.

Intervening in the International Court of Justice case brought by Australia against Japan on Monday, the NZ Attorney-General, Chris Finlayson, said the treaty's purpose was not the protection of commercial whaling.

High stakes battle: Sea Shepherd ship Steve Irwin closes in on the Japanese research vessel Nisshin Maru earlier this year. Credit:Reuters/Sea Shepherd

Instead Mr Finlayson told the ICJ in The Hague that the International Convention for the Regulation of Whaling was intended to be for the conservation and development of whale stocks.

Its key article eight on "special permit" scientific whaling, which is being argued before ICJ, did not give carte blanche to any member country to sidestep the rest of the treaty, he said.