Sea Shepherd is considering appealing a contempt of court finding in the US that could see the activist group ordered to pay up to $US2 million ($A2.16 million) to Japanese whalers.

The radical environmentalists, who threw acid and smoke bombs at their targets, were found in contempt of court on Friday for continuing their relentless campaign to disrupt the annual whale hunt off the waters of Antarctica.

The 9th US Circuit Court of Appeals has ordered a commissioner to determine how much the Sea Shepherd Conservation Society and founder Paul Watson owe as a result of violating an order to stop their dangerous protests.

The whalers are demanding $US2 million ($A2.16 million) in addition to lawyer's fees and damage to their ships.

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Sea Shepherd said in a statement it is disappointed with the ruling and considering its legal options.

"We are considering our legal options at this time, including the possibility of an appeal," it said.

The environmentalists' exploits have been documented on the Animal Planet reality TV series Whale Wars.

In 2012, the court ordered them to stay at least 150 metres from Japanese whalers and halt activities like attempting to ram them and throwing smoke bombs and bottles of acid.

The group also drags metal-reinforced ropes in the water to damage propellers and rudders, launches flares with hooks and uses high-powered lasers to annoy whaling crewmen.

The whalers filed a lawsuit in Seattle in 2011 seeking to halt the Sea Shepherd campaign, prompting the 9th Circuit to order a stop to the harassment but Watson transferred all US assets to foreign entities controlled by the group.

Sea Shepherd has organisations in Australia, Belgium, France, Germany, the Netherlands and Britain.

Watson also stepped down as a director in the US and Australia and resigned as captain of the Sea Shepherd's flagship the Steve Irwin but remained aboard as an "observer".

In February 2013, the 9th Circuit appointed a commissioner to investigate whether he and members of the group should be held in contempt.

The commissioner concluded they weren't in violation because their campaign was being managed outside the United States.

However, a three-judge panel rejected the findings on Friday, ruling that the transfer of assets and control to other countries didn't change its order to cease dangerous activities.