A federal appeals court has declared Sea Shepherd Conservation Society as modern-day pirates and ordered the anti-whaling activists to halt their “aggressive” confrontations of Japanese ships in the waters off Antarctica.

On Monday, the 9th US Circuit Court of Appeals ruled that Japanese whalers – who catch the creatures, Sea Shepherd says, under the guise of “scientific research” – could continue with their federal lawsuit seeking to permanently ban founder Paul Watson and the Sea Shepherd Organization, according to AP.

Chief Judge Alex Kozinski said that the militant conservationists were threatening the lives of whalers, calling their tactics “the very embodiment of piracy”.

“You don’t need a peg leg or an eye patch,” Kozinski wrote for the three-judge panel. “When you ram ships; hurl glass containers of acid; drag metal-reinforced ropes in the water to damage propellers and rudders; launch smoke bombs and flares with hooks; and point high-powered lasers at other ships, you are, without a doubt, a pirate, no matter how high-minded you believe your purpose to be.”

The ruling rebuked US District Judge Richard Jones who dismissed a lawsuit filed by a group of Japanese whalers seeking a court-ordered suspension to the protesters’ aggressive tactics.

It also ordered the lower-court judge in Seattle who had sided with Sea Shepherd removed from the case.

Japanese whalers and the conservationists clashed in icy waters from Antarctica on Monday, with both sides accusing the other of ramming their vessels, AFP reported.

Sea Shepherd founder Paul Watson said the Japanese factory ship Nisshin Maru rammed the protester’s much smaller vessel.