The annual whaling season battle between activists and Japanese whalers kicked off on Wednesday.
Japanese whaling body the ICR said its vessel was harassed by a Sea Shepherd boat on the high seas for five hours.
But the U.S. based activist group claims the vessel used undue force after firing high powered water cannons at their rubber boat.
Speaking in Australia, the captain of another Sea Shepherd boat said the Japanese whalers - not their organisation - are violating international laws.
(SOUNDBITE) (English) CAPTAIN OF THE STEVE IRWIN, SEA SHEPHERD CONSERVATION SOCIETY, PAUL WATSON:
"You know it has to be kept in mind that Sea Shepherd has not broken a single law in the Southern Ocean. We haven't injured anybody. So, all of this rhetoric from Japan about eco terrorism. The real eco terrorists are people who are going down there and targeting endangered whales in an established international whale sanctuary in violation of an international moratorium on whaling, and now they're burning heavy fuel below 60, which is also a violation of international law. These people are criminals."
Japan introduced scientific whaling to skirt a ban on commercial whaling under a 1986 moratorium.
Last year Japan cut its whaling season short after being harassed by Sea Shepherd, who have been widely criticised for their methods.
Simon Hanna, Reuters.