The Washington-based Center for Science in the Public Interest accuses Coke of selling what is says is basically sugar water by claiming it has vitamins that boost immunity and reduce the risk of disease.
The group said the health benefit claims that Coca-Cola makes about its VitaminWater are ''nonsense.'' It filed a class action lawsuit in U.S. District Court in the Northern District of California.
Coca-Cola bought Glaceau's VitaminWater for $4.1 billion in June 2007. At the time, it was considered a coup for the company, which was competing for customers who were buying less and less soda.
VitaminWater has been good for Coke's bottom line since the acquisition, with sales rising by a double-digit percentage in the third quarter.
''It truly shocks the conscience that a company like Coke would try to keep customers by selling them a soft drink and telling them it's a vitamin,'' said Stephen Gardner, director of litigation for the group.
Coca-Cola did not immediately return a call seeking comment.
The same advocacy group sued MillerCoors last fall to stop the brewer from selling Sparks, an alcoholic energy drink. Last month the company agreed to remove some stimulants from its formula.
Shares of Coke fell 1 cent to $42.61 in late morning trading.