Conservation groups have accused the Japanese whaling fleet of ignoring international law as the fleet prepares to head off on its annual whale hunt.

Every November the Japanese whaling fleet heads to the Southern Ocean for its so-called scientific research program.

This year the quota includes 935 minke whales and 50 fin whales.

Three years ago, 50 humpbacks were added to that quota but are yet to be included in the cull.

International Fund for Animal Welfare spokesman Patrick Ramage says humpbacks could be the target this year.

"What they've essentially done is said 'one false move in these ongoing discussions and the humpback gets it'," he said.

"They've used the threat of killing humpback whales to leverage outcomes at the negotiating table.

"Fifty humpbacks remain under threat as the fleet departs Japan this year for the sanctuary."

Mr Ramage says killing whales in a marine sanctuary is illegal under international law.

"It's absolutely unacceptable that Japan is continuing to harpoon them, doubly so that it's in an international sanctuary," he said.

But the spokesman for the Japanese Institute of Cetacean research, Glenn Inwood, has rejected the accusations.

He says the cull is in the name of science.

"A sanctuary doesn't apply to research whaling," he said.

"That's been accepted by the Australian Government, the New Zealand government and also the rest of the International Whaling Commission."

The Federal Government is taking Japan to the International Court of Justice over its whaling practices, but formal proceedings are not expected to be heard until next year.