Burger King was brought to trial by a vegan customer who accused the fast-food chain of contaminating its meatless ‘Impossible Whoppers’ by cooking them on the same grills as its traditional meat burgers.

Phillip Williams purchased the Impossible Whopper at a drive-thru store in Atlanta after reading about the Impossible Burger online.

He bought the vegan Whopper, which costs around $1 more than the regular Whopper.

Being a strict vegan who doesn’t eat any animal byproduct, Williams studiously checked that the burger was indeed mayonnaise free and proceeded to eat it.

He says he was shocked to find later on that the Impossible Whopper is cooked on the same grills as the meat.

Williams alleges that no signage on his trip warned him that his burger would be cooked on the same grills as the meat, nor was he notified by any staff before he ate it.

The lawsuit filed in Miami federal court seeks damages for all U.S. purchasers of the Impossible Whopper, and an injunction requiring Burger King to “plainly disclose” that Impossible Whoppers and regular burgers are cooked on the same grills.

Burger King, a unit of Toronto-based Restaurant Brands International Inc, declined to comment, saying it does not discuss pending litigation.

Its website describes the Impossible Burger as “100% Whopper, 0% Beef,” and adds that “for guests looking for a meat-free option, a non-broiler method of preparation is available upon request.”

Williams’ lawyer did not immediately respond to a request for comment on the disclaimer or the available cooking options.

Burger King began selling the Impossible Whopper in August.