A group of consumers is suing Starbucks and accusing the coffee chain of wrongly marketing its line of "Protein Beverages" as free of sugar.

The class action case filed by three consumers on behalf of a proposed class of Starbucks customers alleges that eight beverages whose names began with the words "sugar-free" in fact contained lactose, a naturally-occurring sugar in milk. The suit was filed on Friday in the U.S. District Court for the Western District of Washington.

The plaintiffs also alleged that Starbucks failed to include a disclaimer around the drinks' calorie contents as required by the Food and Drug Administration.

The drinks at the center of the lawsuit are the Sugar-Free Vanilla Protein Latte, the Sugar-Free Caramel Protein Latte, the Sugar-Free Vanilla Protein Matcha, and the Sugar-Free Caramel Protein Matcha, as well as each drink's respective iced version.

The plaintiffs alleged that the drinks contained between 13 grams and 21 grams of sugar per venti serving based on their milk content, well above the maximum sugar content allowed for a "sugar-free" drink under the FDA's regulations.

"No reasonable consumer would understand a beverage named 'Sugar-Free' to contain 13 to 21 grams of sugar per serving," according to the lawsuit.

Starbucks did not immediately respond to a request for comment.

The plaintiffs are alleging that Starbucks has violated false advertising laws in New York, California, and Washington, where the company is headquartered. They are requesting damages and restitution.