The Sea Shepherd Conservation Society says a report by Maritime New Zealand, on a collision between a protest boat and a Japanese whaling ship in the Southern Ocean in January, is a waste of time.
The report found no evidence that either the Shonan Maru 2, or the Ady Gil set out to cause a collision.
Sea Shepherd president Paul Watson dismissed the findings. He says the report cannot be conclusive because the Japanese captain refused to be interviewed.
Maritime New Zealand says it is satisfied the report is sound and robust.
Meanwhile, Japan's Institute of Cetacean Research says the report vindicates Japan's efforts against what it calls a terrorist group on the high seas.
The whaling season is due to start next month. The institute says this year's catch could include up to 850 minke whales and 50 finn whales.