An animal rights group has sued SeaWorld, accusing the aquatic theme park chain of violating the rights of captive killer whales under the 13th Amendment of the US Constitution, which abolished slavery.
The lawsuit, filed late on Tuesday in US District Court in San Diego, lists five performing orcas at SeaWorld's parks in California and Florida - Tilikum, Katina, Corky, Kasatka and Ulises - as plaintiffs in the complaint.
"All five of these orcas were violently seized from the ocean and taken from their families as babies," Ingrid Newkirk, president of People for the Ethical Treatment of Animals (PETA), said in a statement.
"They are denied freedom and everything else that is natural and important to them while kept in small concrete tanks and reduced to performing stupid tricks," she said.
SeaWorld San Diego responded with its own statement saying PETA's efforts to "extend the Thirteenth Amendment's solemn protections beyond human beings is baseless and in many ways offensive."
The park, the first of three established by SeaWorld Parks & Entertainment, added that displaying the marine mammals in captivity educates the public about the creatures.
David Steinberg, a professor at the Thomas Jefferson School of Law in San Diego, characterized as "patently, absolutely frivolous" PETA's claims that whales are entitled to protection from involuntary servitude under the 13th Amendment, ratified in 1865.
"The 13th Amendment abolished the abhorrent, despicable practice of the slavery of human beings," he told Reuters. "PETA is demeaning the integrity and humanity of people who were owned as slaves. That is outrageous."
The lawsuit seeks a court order requiring SeaWorld to release the five killer whales to a "suitable habitat."
Four of the orcas were caught in the wild off the coast of Iceland and a fifth was captured off the Pacific Northwest, the suit says. One of the whales, Tilikum, killed a trainer in Orlando last year by dragging her underwater.
The suit lists PETA and two former SeaWorld employees who have become activists opposing the captivity of marine mammals as "next friends" bringing suit on behalf of the whales.
PETA has undertaken a number of controversial actions in the past in seeking to advance the cause of animal rights.
Last year, a PETA member struck a Canadian government minister in the face with a pie to protest seal hunting. In 2003, the Anti-Defamation League accused PETA of trivializing the deaths of Jews in World War Two with a campaign that compared the meat industry to the Holocaust.
Virginia-based PETA's profile has risen in recent years with its "I'd Rather Go Naked Than Wear Fur" campaign, which has enlisted celebrities to pose nude for the group.