The anti-whaling activist and founder of the Sea Shepherd Conservation Society Paul Watson is due to take the witness stand in a contempt of court hearing in Seattle.
Japan’s Institute of Cetacean Research brought the case before the US courts and claims Sea Shepherd has broken a US ruling which says ships must remain 457 metres from whaling vessels at all times.
The Japanese want the court to impose heavy fines on the anti-whaling organisation but said they would be willing to waive them if the protesters stop their action.
Sea Shepherd denies it broke the order and says it is their Australian namesake which confronted the whalers.
Watson and his group are well known for their high sea clashes in the Antarctic Ocean with Japanese fishing fleets. The 62-year-old Canadian has been on the run from authorities in three countries since May 2012 when he was detained in Germany on a Costa Rican extradition warrant. Japan was also seeking his extradition from Germany.
He skipped bail and German authorities issued a warrant for his arrest.