In what has been called an 'unprecedented' legal action, People for the Ethical Treatment of Animals (PETA) is filing a lawsuit against SeaWorld that accuses it of keeping five killer whales in conditions that violate the 13th Amendment ban on slavery.
A federal court is being requested to grant the animal constitutional rights, an action that has sparked further debate over the expansion of animal rights.
The plaintiffs are the five orcas, Tilikum and Katina based at SeaWorld in Orlando, Florida, and Corky, Kasatka and Ulises at SeaWorld San Diego.
The lawsuit asks the court to order the release of the orcas to the custody of a legal guardian, who would then find a 'suitable' habitat for them.
PETA's general counsel, Jeff Kerr, whose five-strong team spent 18 months working on the case, told news.com.au: 'By any definition, these orcas are slaves - kidnapped from their homes, kept confined, denied everything that's natural to them and forced to perform tricks for SeaWorld's profit.
'The males have their sperm collected, the females are artificially inseminated and forced to bear young which are sometimes shipped away.'
Under US laws, animals under human control are considered property and do not currently have legal standing of their own.
They are protected by animal cruelty laws like the federal Animal Welfare Act, but do not have an outlined set of rights.
The field of animal law is, however, evolving. Rutgers University law professor Gary Francione, for example, suggests that animals deserve the fundamental right to not be treated as property.
Law professor David Favre of Michigan State University has proposed a new legal category called 'living property' as a step toward providing rights for some animals.
SeaWorld, meanwhile, said efforts to extend the 13th Amendment's protections beyond humans 'is baseless and in many ways offensive'.
The company added: 'SeaWorld is among the world's most respected zoological institutions. 'There is no higher priority than the welfare of the animals entrusted to our care and no facility sets higher standards in husbandry, veterinary care and enrichment.'
The statement also highlighted the company's 'global efforts to promote conservation of marine mammals', and said the orcas' performances 'help give the public a better appreciation and understanding of these animals'.
The six-tonne male at SeaWorld in Orlando, Tilikum, hit the headlines earlier this year when he grabbed a trainer at the end of a performance and dragged her underwater to her death.