The U.S. Fish and Wildlife Service said it will review allegations that Donald Trump Jr., may have illegally killed a rare sheep during a recent trip to Mongolia and imported parts of the animal back to the U.S.

Animal conservation activists said President Donald Trump’s eldest son may have violated a federal wildlife anti-trafficking law after ProPublica reported last week that he shot and killed an argali sheep without proper permits during a personal trip in August. The Mongolian government issued a permit for hunting the sheep after the fact, and it’s unclear what happened to the animal after it was killed, according to the report.

A spokesperson for Trump Jr. on Tuesday provided a statement to CQ Roll Call denying allegations of wrongdoing related to the hunting permit. In the statement, which was also provided to ProPublica, the spokesperson said the hunting trip was purchased in 2015 at a National Rifle Association auction before his father announced his presidential campaign and all permits were secured through a third-party hunting group.

Trump Jr.’s spokesperson declined to comment on whether any argali animal parts were imported to the U.S.

The Center for Biological Diversity, in a Dec. 13 letter, asked FWS law enforcement to evaluate whether the reported hunt and retroactive permit violated any U.S. or Mongolian laws. Under the Lacey Act of 1900, it is illegal to import animal trophies in contravention with foreign laws and individuals found in violation can be subject to fines and prison time.

In its letter the group also asked if there were any permits pending to import the animal that Trump allegedly killed and noted the argali sheep population in Mongolia is protected under the Endangered Species Act and a 1975 international treaty governing wildlife trafficking. (roll call)