A case is being prepared against the distributors of QuickTrim and marketing claims made by the Kardashians.
QuickTrim is a weight-loss supplement that's not approved by the Food and Drug Administration.
The Kardashian sisters claimed they used it to lose 15 pounds in weeks.
Opponents say QuickTrim contains high levels of caffeine and ingredients that aren't safe or effective for weight loss.
The Kardashians have not commented on the case.