Environmental group Sea Shepherd has accused the Japanese whaling fleet of ramming one of its vessels in the Southern Ocean.
Sea Shepherd says its ship the Bob Barker was deliberately struck by the Yushin Maru No. 2 early on Sunday morning (AEDT).
Sea Shepherd Australia spokesman Adam Burling told AAP no structural damage was done, but the strike would likely delay the Bob Barker in its anti-whaling efforts.
Mr Burling said the strike was in retaliation for the Sea Shepherd preventing any whales from being captured for more than a week.
The commercial hunting of whales is banned in the Southern Ocean Whale Sanctuary, but Japan catches the mammals under a "scientific research" clause in the moratorium.
Comment is being sought from Japan's Institute of Cetacean Research.
