Anyone who recently proposed to his or her significant other with a Tiffany & Co. engagement ring might want to double-check that it’s the real deal.

Yesterday (coincidentally on one of the most romantic days of the year), Tiffany filed suit against Costco Wholesale Corp. accusing it of selling counterfeit versions of its diamond engagement rings. According to the complaint, Tiffany only sells its jewelry at its own stores, and Costco isn’t authorized to sell Tiffany items.

Last November, a customer in California alerted Tiffany that the discount retailer was selling rings under the Tiffany name. “Costco had apparently been selling different styles of rings for many years that it had falsely identified on in-store signage as ‘Tiffany,’” thus leading customers to believe that they were buying authentic Tiffany items, the suit says.

“We now know that there are hundreds if not thousands of Costco members who think they bought a Tiffany engagement ring at Costco, which they didn’t,” Jeffrey Mitchell, a lawyer for Tiffany, said in a statement. “Costco knew what it was doing when it used the Tiffany trademark to sell rings that had nothing to do with Tiffany.”

Tiffany seeks to find out the exact number of counterfeit rings Costco sold, as well as to prevent further sales of such rings and unspecified damages.

This isn’t Costco’s first experience with counterfeit claims. In 2011, a federal jury found the retailer guilty of trademark violation for selling fake versions of Farouk Systems Inc.’s CHI flat irons.

Read the Wall Street Journal for more about Tiffany’s suit against Costco.

For more recent InsideCounsel stories concerning legal battles in the luxury goods world, read:

2nd Circuit sides with Ralph Lauren in polo player logo fight

YSL seeks to dismiss counterclaims against Louboutin

Louis Vuitton loses lawsuit over knockoff handbag in “The Hangover: Part II”

Counterfeit Louis Vuitton handbags infringe company’s IP

Chanel seizes rogue websites’ domain names