Greens leader Bob Brown has described three Australian activists detained on board the Japanese whaling security vessel Shonan Maru No 2 as "heroic".
"These three Australians are heroes for the whales," Senator Brown said on Monday.
"And they've come from a forest protest background from trying to protect the biggest living entities on the planet land to trying to protect the biggest living creatures in the ocean."
Senator Brown said the trio are "terrific Australian citizens and they deserve a huge amount of support".
The West Australian men from the Forest Rescue environmental group boarded the Shonan Maru No 2 off the coast of Bunbury on Saturday night.
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They were aiming to force the vessel to stop tailing the Sea Shepherd Conservation Society's anti-whaling flagship, the Steve Irwin.
The activists had demanded to be returned to Australia, but on Monday the Japanese vessel was travelling towards the whaling areas of the Southern Ocean. They have been named as Geoffrey Owen Tuxworth, 47, of Perth, Simon Peterffy, 44, of Bunbury, and Glen Pendlebury, 27, of Fremantle.
Senator Brown said he had written to Opposition Leader Tony Abbott to seek the coalition's support for a proposed Greens bill that would require an Australian customs vessel to be present when whaling is taking place in Australia's territorial waters.
"This is a case where the opposition and Greens can work together to have the government do what it's failing to do," Senator Brown said.
"We have the numbers in the parliament, I believe, to make that a legislative requirement."
Mr Abbott could agree to Senator Brown's request, after earlier on Monday saying Australia should send a customs vessel to "keep the peace" in the Southern Ocean. Attorney-General Nicola Roxon has been in contact with the Japanese government.
Ms Roxon has said the issue involving the three activists has been complicated because the boarding didn't happen in Australia's territorial waters, meaning they would subject to Japanese laws.
