The manufacturers of Skinnygirl Margarita, a drink conceived by one of the “Real Housewives of New York City,” are facing a class-action suit in New Jersey that alleges the product is falsely claimed to be an all-natural, preservative-free and healthy alternative to other margarita mixes.

Contrary to company advertisements, the drink contains sodium benzoate, a chemical preservative that — when mixed with citric acid in the lime juice commonly added to margaritas — can be carcinogenic, the plaintiffs allege in Stewart v. Beam Global Spirits & Wine Inc., 11-cv-5149, which has just survived its first dispositive motion ruling.