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.