The accusation comes in a trademark lawsuit filed in Manhattan federal court on Valentine’s Day.
The suit demands that Costco pay Tiffany profits from the bootleg rings, and millions in damages.
Tiffany said it believes “hundreds, if not thousands, of Costco members bought engagement rings they believed were authentic Tiffany products but were not.”
Costco was allegedly selling the counterfeits in stores labeled with the Tiffany brand with salespeople referring to them as Tiffany rings.
But Tiffany said when Costco sold the same designs online they didn’t use the Tiffany name because their fraud would be more easily discovered. The suit says Costco has been perpetrating the fraud for years.
“This is not the kind of behavior people expect from a company like Costco, and this case will shed a much needed light on this outrageous behavior,” Jeffrey Mitchell, a lawyer for Tiffany told Reuters.