McLEAN, Va. — An animal-rights group sued the U.S. Fish and Wildlife Service on Friday to stop a policy it says allows trophy hunters, circus acts and others dealing with threatened species to skirt the Endangered Species Act by making token donations to conservation groups.

The lawsuit, filed in U.S. District Court in Alexandria by Norfolk-based People for the Ethical Treatment of Animals, alleges that the wildlife service is sanctioning a massive loophole in the Endangered Species Act. The law allows exceptions in the import or export of endangered species when granting a permit aids the species’ survival. PETA says the agency is granting exceptions for applicants making donations as small as $500 to conservation groups.

A Fish and Wildlife spokeswoman said the agency can’t comment on active litigation.

An auction earlier this year of a permit to hunt an endangered black rhino in Namibia is an example of how the policy has run amok, PETA said. Hunter Corey Knowlton bid $350,000 last year to win an auction conducted by the Dallas Safari Club to hunt and kill a rare black rhino in Namibia. The Fish and Wildlife Service granted Knowlton an exception allowing him to import the carcass back to the U.S. as a trophy, under the theory that the money paid to Namibia will help that country carry out its preservation efforts.

More often, though, said PETA Foundation Counsel Delcianna Winders, circus acts take advantage of the loophole to be able to move tigers and elephants across U.S. borders. Winders said PETA does not know exactly how many times applicants have obtained permits by making donations.

It cites another example of a circus being granted a permit to take two endangered elephants from the U.S. into Canada for performances there by making a $500 donation to a group called Asian Elephant Support.

Winders said the exception in the law is designed to allow importation or export for circumstances like releasing an animal into the wild or supporting a breeding program. Instead, she said the donations amount to a pay-to-play scheme that perverts the intention of the law.

“It’s almost like auctioning off a child on the black market and saying it’s OK because the some of the money is going to an anti-trafficking group,” Winders said.

The Fish and Wildlife Service had previously said it permitted the importation of the rhino trophies because Namibia has a comprehensive strategy in place to protect black rhinos, and the money paid to that country will support those efforts.

The safari club’s executive director was traveling and unavailable for comment Friday. The club said the money helped conservation efforts and that targeted hunting of a small number of older male rhinos can actually help the overall herd.