The FDA is warning the Coca-Cola Company that one of its products contains inappropriate nutritional claims.

The U.S. Food and Drug Administration wrote a letter on Dec. 10 to the soft drink giant, warning it about the “misbranded” Diet Coke Plus, a drink released in the United Kingdom in October 2007, available in two variants, one with vitamins B3, B12, and vitamin C, and the other one containing antioxidants with extra green tea and vitamin C.

Federal regulators claim that the label of the drink infringes the agency’s guidelines for using the term "plus" and claiming that it is a source of vitamins and minerals. The item indeed contains zinc, magnesium and vitamin B, but the quantities are unquestionably insufficient to make the nutritional claims, the FDA said, adding that that foods labeled "plus" ought to have at least 10 percent more nutrients than comparable products.

In the letter, posted on the FDA website on Tuesday two weeks after it was dated, the agency gave the company 15 days to tell how it plans to fix the violation of the Federal Food, Drug and Cosmetic Act, a set of laws passed in 1938 which lays down the conditions in which a company is allowed to make nutritional and health claims.

"Your Diet Coke Plus product is mislabeled... .because the product makes a nutrient content claim but does not meet the criteria to make that claim," federal regulators wrote in the letter.