McDonald should stop marketing junk foods to kids and retire its corporate symbol Ronald McDonald, say opponents.
The letter comes a day before the fast food giant's annual meeting in Chicago at which a group of nuns have proposed that McDonald's issue a report assessing its response to "public concerns regarding linkages of fast food to childhood obesity."
The open letter urged McDonald's to go even further and stop offering toys with meals high in salt, fat, sugar and calories.
It is part of a two-year campaign by Corporate Accountability International, a non-profit best known for its campaign to retire cigarette mascot Joe Camel.
The clown character Ronald McDonald -- sporting oversized red shoes and yellow rompers emblazoned with the restaurant chain's "Golden Arches" logo -- for decades has been used by McDonald's as a kid-friendly corporate spokesman.
McDonald's defended its iconic mascot, its food offerings and its record on responsible advertising.
"As the face of Ronald McDonald House Charities, Ronald is an ambassador for good and delivers important messages to kids on safety, literacy and balanced, active lifestyles," McDonald's said in a statement.
"We serve high quality food, and our Happy Meals offer choice and variety in portions just for kids. Parents tell us they appreciate our Happy Meal choices."