An animal rights group has sued SeaWorld on behalf of its whales under an American law abolishing slavery.
People for the Ethical Treatment of Animals (PETA) claim the chain of theme parks violate the rights of killer whales under the 13th Amendment of the US Constitution.
Five performing whales at SeaWorld - Tilikum, Katina, Corky, Kasatka, and Ulises - are listed as plaintiffs in the complaint.
"All five of these orcas were violently seized from the ocean and taken from their families as babies," said PETA president Ingrid Newkirk.
"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 labelled the lawsuit, filed in the city on Tuesday, as "offensive".
A park statement said that PETA's efforts to "extend the Thirteenth Amendment's solemn protections beyond human beings is baseless and in many ways offensive."
David Steinberg, a professor at the Thomas Jefferson School of Law in San Diego, called the suit "patently, absolutely frivolous".
"The 13th Amendment abolished the abhorrent, despicable practice of the slavery of human beings," he said.
"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".
One of the whales, Tilikum , killed a trainer in Orlando last year by dragging her underwater. The incident raised an outcry about safety and animal rights.
The suit lists PETA and two former SeaWorld employees who have become activists opposing the captivity of marine mammals as "next friends" bringing the suit on behalf of the whales.
PETA, famous for its "I'd Rather Go Naked Than Wear Fur" campaign, has undertaken a number of controversial actions in the past in seeking to advance the cause of animal rights.