A member of anti-whaling group Sea Shepherd Conservation Society says his vessel has been rammed several times by a Japanese whaling ship.
Four Sea Shepherd vessels set sail for the Southern Ocean in January, saying they wanted to prevent the Japanese fleet from taking a single whale.
Peter Hammarstedt, captain of the Bob Barker, told Radio New Zealand's Checkpoint programme on Wednesday that his ship and another Sea Shepherd vessel, the Steve Irwin, were hit while blocking the whalers refuelling from an oil tanker.
He said the Japanese factory ship Nisshin Maru rammed his ship four times, damaging its wheelhouse, radar and helicopter flight deck.
Mr Hammarstedt says no one was hurt, but believes the Bob Barker could have been rolled over completely if the Nisshin Maru had continued to ram it.
The Sea Shepherd ships plan to continue blocking the whalers from refuelling, he said.
This incident follows the sinking of Sea Shepherd vessel, the Ady Gil, in 2010 which happened as a result of a confrontation with a whaling ship.
Meanwhile, Sea Shepherd director Bob Brown wants the Australian government to call in the navy to break up a clash between the conservationists and the Japanese fleet.
The former Australian Greens leader says he wants immediate action against what he calls "multiple breaches of international law", the ABC reports.
Mr Brown says crew members also say Japanese coastguards on board one of the whaling boats told them to leave the area and then began throwing concussion grenades towards them.
He wants the Australian government to urgently intervene, but Environment Minister Tony Burke says he is still trying to confirm what happened.
In December last year, a United States court ordered Sea Shepherd to stay at least 450 metres away from Japanese whaling ships.
Japan claims that its whaling programme is for scientific research.