Katy Perry has her name plastered on anything for a buck -- she's had deals with Wal-Mart, Cover Girl, Eyelure Eyelashes, PopChips, ProActiv, Adidas, GHD, OPI -- but it's her deal with Pepsi that's getting people's panties in a twist.

Health groups have purchased a full-page ad in Variety begging Perry to drop her deal with the soft drink giant, which has also sponsored celebs like Beyonce, Pink, Britney Spears, Nicki Minaj and One Direction.

An open letter to the 'Prism' singer claims, "Today soda companies are using you and other celebrities to convince young people that drinking soda is hip, sexy and rebellious. That's certainly the case with Pepsi's promotions in connection with your concert and forthcoming album," the letter continues. "'Drink Pepsi and you can be cool like Katy Perry' is the takeaway message for your young fans. 'Live for now' -- and worry about the health consequences later."

The groups protesting Perry's Pepsi endorsement are the Center for Science in the Public Interest, California Center for Public Health Advocacy, California Pan-Ethnic Health Network, Latino Coalition for a Healthy California, Berkeley Media Studies Group, CCFC and the California Endowment.

Ouch! You can read the full letter below -- but uh, where were these people when Perry released 'Last Friday Night,' an ode to binge drinking?