Burger King’s beef-free Whopper may not be so meatless after all — at least according to one vegan customer.

That’s the argument being made in a lawsuit filed on Monday in the United States District Court for the Southern District of Florida, in which the plaintiff, Phillip Williams, claims that the fast food chain failed to disclose that its plant-based Impossible Whoppers are cooked on the same grills as beef products.

The class-action suit accuses Burger King of undertaking “false and misleading business practices” in the marketing and sale of its meatless burgers, and notes that vegans would not purchase the Impossible patties if they knew they had been prepared next to meat options.

Mr. Williams, who practices “a strict vegan diet,” bought an Impossible Whopper at a drive-through in Atlanta in August or around that time, according to court documents. The complaint said that he was “duped by Burger King’s deceptive practices into eating a meat-free Whopper Patty that was in fact covered in meat byproducts,” though it did not specify how he came to know this was the case.