Wellington, May 24 NZPA - New Zealand and Australia can win an International Court of Justice (IJC) case against Japan over its whaling practices, a legal specialist says.

Australia National University international law Professor Donald Rothwell is touring New Zealand this week, talking about legal options open to challenge Japanese whaling before international courts.

The forums were organised by Green Party MP Gareth Hughes.

At Parliament today, Prof Rothwell said New Zealand could join forces with Australia, which has placed a November deadline on Japan to stop whaling or face the ICJ, or head to court alone.

He said there is a strong chance that a case against Japan would succeed.

He was reluctant to speculate as to what a loss would mean.

"If you make your sole legal case that what Japan is doing is not scientific, but commercial whaling, and the international court was to come down with an unfavourable ruling, that clearly would be undesirable.

"But I'm doubtful the international court would say that. Even if you would conceive that it would be a loss, the court would have to say well there are limits to what you can take for scientific purposes.

"They might have to put some sort of number on what those would be."

The International Whaling Commission (IWC) released a proposal last month that would allow Japan, Norway and Iceland to continue commercial whaling for another decade, despite a global ban.

The environmentally delicate Southern Ocean would be designated as a sanctuary, but whalers from Japan would still be allowed to take a number of the marine mammals from the seas around Antarctica.

The Government was unimpressed with the proposal, and Foreign Minister Murray McCully said it would continue with the diplomatic process though he added, if all failed, the Government might consider ICJ route.

The proposal will be decided on at the next IWC meeting in June in Morocco.

Mr Hughes said taking Japan to international court should be considered.

"We should use all the tools," he said.

"Australia has been very strong is saying they'll do it if the diplomatic process falls over.

"I think we're heading up to a failure in Morocco next month.

"Our Government said some aspects are unacceptable. We still don't know what the Government's clear bottom lines are and what they are prepared to compromise."