A vegan customer sues Burger King for preparing his vegetable patties on the same barbecues as the meat.
In a class action lawsuit filed in the US, Philip Williams said the way the Impossible Whopper is being grilled is "covered with meat by-products."
He said the burger's slogan – "100% Whopper, 0% Beef" – was misleading.
Burger King did not comment on that, but the fine print on its website tells people If you want a meat-free option, you can request "a broiler-less preparation method".
A spokeswoman for supplier Impossible Foods told Reuters that vegetarians and vegans are "happy" to ask about their Impossible Whopper in the microwave.
In a lawsuit in Miami, Mr. Williams says the burger chain does not clearly announce that the plant-based burgers are cooked with meat.
He said he had taken a drive-through restaurant in Atlanta, Georgia, and ordered the Impossible Whoppe r without mayonnaise.
At no time was he informed that the Whopper was being cooked on the same grill as the Fleischburger. Had he known, he would not have ordered it.
Mr. Williams said he wanted compensation for anyone in the US who bought the Impossible Whopper, as well as a restraining order from Burger King to "make it clear" that the vegan burgers and meat burgers are being prepared on the same grills.
Burger King began selling the Impossible Whopper in Sweden in May, before being shipped to US stores in August. The sale of the meatless Burgers began earlier this month in 25 other European countries.
According to Burger King, the plant-based burger costs US customers about $ 1 more than the beef version.