Four governments, including New Zealand's, have issued a warning to Sea Shepherd and Japanese whalers to behave in the Southern Ocean this whaling season - just days after a US court issued an injunction against the protest group.
In a joint statement, the New Zealand, Australian, US and Netherlands governments condemned "any actions that imperil human life at sea", calling for the masters of all vessels to ensure their crews' safety and follow international rules to avoid collisions.
"We respect the right to peaceful protest, including on the high seas. We condemn dangerous or unlawful behaviour at sea by any party in the Southern Ocean or elsewhere," the governments said, warning that they were prepared to prosecute anyone engaging in unlawful behaviour.
The Government says it is "resolutely opposed" to commercial whaling, including Japan's so-called scientific whaling.
The statement was issued after a US appeals court this week issued an injunction ordering Sea Shepherd and its head Paul Watson not to physically attack or endanger the whaling ships, and to remain at least 450 metres from them at all times.
The order was sought by the Institute of Cetacean Research (ICR), which undertakes the Japanese government's whaling programme through a loophole in International Whaling Commission rules that allows whales to be killed for research.
The two sides have previously clashed, with protesters throwing glass bottles containing paint or butyric acid at the whaling ships, and the whalers responding with water cannons.
Former Sea Shepherd member, New Zealander Pete Bethune, spent time in a Japanese jail after boarding the Shonan Maru No 2 after it collided with Sea Shepherd's Ady Gil in 2010.
Mr Watson is back at the helm of the militant conservation group's ship the Steve Irwin, after skipping bail in Germany in July.
He is wanted in Japan and Costa Rica on charges relating to an anti shark-finning protest in 2002.