A consumer lawsuit is accusing Starbucks of adding sugar, sometimes as much as that in a Kit Kat bar, to drinks marketed as sugar free.

The products in question include hot and iced protein lattes and protein matcha beverages in vanilla and caramel flavors. According to the federal lawsuit filed Friday, these drinks contain 13 to 21 grams of sugar per serving.

“No reasonable person” would expect something labeled “sugar-free” to contain that much sugar, the lawsuit contends.

“This case is about false and misleading product names. It is not about missing nutritional information,” according to the lawsuit.

Starbucks denied misleading consumers with its menu in a statement to NBC News on Tuesday. The international coffee chain said it has “consistently and clearly provided information about its protein beverages, sugar-free options, customization choices, and nutritional content across product announcements, menus, marketing materials, Starbucks.com and the Starbucks app, and we intend to vigorously defend ourselves in this matter.”

Hagens Berman filed the suit on behalf of three individual consumers who bought Starbucks’ sugar-free protein drinks in California, New York and Washington, The Associated Press reported.

“Consumers avoid sugar for various reasons, whether that be general health, diabetes and blood glucose levels or other factors, and for many, a staunch mislabeling like this is significant,” Steve Berman, a co-founder and managing partner of the Seattle-headquartered firm, told the AP.

Seattle-based Starbucks said the sugar in its protein drinks comes from the protein-boosted milk it uses. The company said it doesn’t add sugar to the drinks and it uses sugar-free syrup for flavoring.

On Starbucks’ website Monday, the drinks were marketed as “sugar-free,” but the company also stated the amount of sugar in each beverage and that they were made without added sugar.

The lawsuit seeks damages on behalf of U.S. consumers who bought the drinks. It also wants the court to order Starbucks to stop using the label “sugar-free” on products that contain sugar.