Australia has joined forces with New Zealand, the US and the Netherlands to call for responsible behaviour during the Southern Ocean whaling season.
The anti-whaling nations said in a joint statement that they respected the right to peaceful protests, but would use the force of the law against any "unlawful activity".
They urged activists not to take any action endangering human life as Japan's first fleet prepared to set sail for its controversial annual hunt.
The four nations reiterated that they were "resolutely opposed" to whaling in the waters, which the International Whaling Commission has declared to be a sanctuary.
"Lethal research techniques are not required in modern whale conservation and management," the commission's statement said.
US-based environmental group Sea Shepherd each year disrupts the expeditions of Japan, which kills whales through a loophole in a 1986 global moratorium that allows "lethal research" on the ocean giants.
Captain Paul Watson said the statement was aimed at Sea Shepherd, whose vessels followed the Japanese whaling fleet each summer to try and disrupt its so-called scientific whaling activities.
"Of course it's aimed at us," Mr Watson said.
"But the Japanese are the only ones who have caused injury out here when we try to block their operations, and we haven't injured any of them or damaged their properties."
Sea Shepherd had vowed to fight a recent injunction from a US court, which, in response to Japan's complaints, ordered the environmentalists to stay at least 500 metres from the ships.
A Japanese official praised the court order and said it would help "the whaling and research mission in the Antarctic Ocean to be conducted safely and smoothly".