The current Labor government of Australia should instigate international court action against the whale-hunting nation of Japan by the end of January, federal opposition environment spokesman Greg Hunt says.

In an open letter addressed to Environment Minister Peter Garrett, Hunt pushed for the government to set a date to commence legal action, or risk losing faith with a disillusioned Australian public.

"I am writing to express my extreme frustration and disappointment that you have once again refused to send a ship to the Southern Ocean to chronicle the annual slaughter of the great whales," he wrote.

"From this I can only assume that you believe you already have sufficient evidence to mount an international court case against Japan."

"The Labor Party has been promising for three years now to take Japan to the International Court of Justice, yet new whaling seasons have continued to roll round without any action."

Hunt called on Garrett to bring the legal action by January 31, with a view to withdrawing the documents if Japan agreed to cease whaling by June 30.