In full-page ads running Wednesday in The New York Times and the Chicago Tribune – the hometown paper of the Illinois-based McDonald’s – the fast-food chain is proposing the “McWhopper,” a hybrid of each company’s signature Big Mac and Whopper burgers that will be sold for one day in one pop-up store in one city.

That city, Burger King is proposing, would be Atlanta, a meeting point between both company’s headquarters. The marketing stunt would be held on Sept. 21, with proceeds benefiting the anti-conflict nonprofit Peace One Day.