The FBI warning, dated May 22 and titled “Federal Hunting License Exception Could Be Exploited by Extremists or Criminal Actors Seeking to Obtain Firearms for Violent Attacks,” was sent from the bureau’s Office of Private Sector, according to a copy reviewed by Yahoo News. The warning encouraged businesses to be aware that “extremists and other criminal actors could exploit the federal statutory exception that allows non-immigrant visa holders” who normally can’t buy firearms or ammunition to legally purchase them “with a valid hunting license or permit.”

The warning goes on to note that foreign “terrorist organizations, including ISIS, have encouraged Westerners to exploit perceived gaps in gun laws to conduct mass casualty shooting attacks in their home countries,” and that foreign national visa holders “could use this hunting license exception to obtain firearms to commit violence in the Homeland.”