The Australian government has announced it will launch legal action against Japan over whaling in the Southern Ocean.
Foreign Minister Stephen Smith says legal papers will be lodged in the International Court of Justice in The Hague next week.
Some legal experts say Japan's whale cull breaches international laws such as the Antarctic Treaty System. A court challenge would lead to so-called provisional orders for Japan to immediately halt whaling ahead of a full hearing.
Commercial whaling has been banned worldwide since 1986 but Japan justifies its annual hunts in the Southern Ocean as lethal "scientific research".
Mr Smith said he informed Japan of the move on Thursday night. "The agreement between Australia and Japan is that we will treat this matter in a calm, responsible, mature way."
Australia would remain closely engaged in the International Whaling Commission, he said, and continue to work to stop whaling in the lead-up to an IWC meeting in Morocco in June, where he admitted chances of an international agreement were "slim", Reuters reports.
Under a compromise deal to be debated by the 88-nation IWC, Japan, Norway and Iceland could be allowed to kill a limited number of whales for the first time in 24 years under a proposal criticised by whaling nations and opponents of the hunts.
The plan would force the trio to cut their quotas for 10 years while the IWC worked out a long-term solution by 2020.
Japan 'disappointed' at move
Japan's Fisheries Minister Hirotaka Akamatsu said Australia's decision is "very disappointing", adding that the country's "research whaling is a programme approved" under the rules of the international ban on commercial whaling.
"I want to continue to argue on that basis," he told reporters on Friday.
In February, Australian Prime Minister Kevin Rudd set Japan a November deadline to halt whaling. Environmentalists have accused him of backpedalling to avoid damaging the country's trade ties with Japan and progress on a free trade deal.
The ABC's correspondent in Tokyo, Mark Willacy, says the Australian and Japanese governments agree that the legal proceedings will not affect relations between them.
"They want to take Japan to court on a very unpopular issue - scientific whaling - but they want to maintain the relationship with the Japanese because it is Australia's largest export trading partner."
He told Radio New Zealand's Checkpoint programme that Japan has suggested that the International Court of Justice may not have jurisdiction over the whaling issue.
NZ prefers diplomatic process
New Zealand says it will only consider joining the Australia's legal action once all diplomatic efforts have failed.
Prime Minister John Key says the legal opinion the New Zealand Government has received is that any court case is not clear cut.
Mr Key believes the diplomatic process is "the best way of seeing a reduction and elimination of whaling.
"In the end, if that diplomatic route is unsuccessful, then New Zealand will make a decision about whether it's going to join Australia in the International Court of Justice."