Have you participated in an online gift exchange? Not only is a police department in Tennessee warning that such exchanges are a scam, it could also be a violation of federal law.

The Cookeville, Tennessee Police Department published a Facebook post on Wednesday encouraging people not to participate in online gift exchanges such as the "Secret Sister" exchange.

The police force cites a federal statute that says, "Any letter, package, postal card, or circular concerning any lottery, gift enterprise, or similar scheme offering prizes dependent in whole or in part upon lot or chance" could lead to a conviction of up to two years in federal prison.

This is because paying $10 in a gift exchange for an unknown number of gifts is considered gambling, and gambling using the mail is illegal.

Also, the police force warns that many of those who participate never get the gifts that they are promised.

"Don’t fall for the post popping up on your news feed about a secret sister gift exchange – it’s a scam and illegal," the post said. "This scam circulated Facebook heavily last year and is making the rounds again this holiday season."

The department's Facebook posting drew a wide-range of responses.

"I wish I knew this last year," Chrystal Phillips said. "Wasted $10."

"I had a lot of fun with this last year," Tiffany Maynard said. "I sure didn't know it was illegal."