The Coca-Cola Co has defended its Diet Coke Plus drink against an allegation by the US Food and Drug Administration that the product breaches the law.

A Coca-Cola spokesperson told just-drinks today (23 December) that it rejected the watchdog's warning, which was sent in a letter to Coca-Cola CEO Muhtar Kent dated 10 December.

Diet Coke Plus cannot use 'plus' in its name because it does not contain sufficient nutrient content, the Food and Drug Administration (FDA) said.

It could ultimately force the firm to rebrand or remove the functional drink from shelves, with the potential reverberations landing a blow on industry attempts to reinvigorate carbonated drinks sales by introducing functional varieties. 

Diet Coke Plus violates FDA policy on fortification of food and drink, enforcement officials said. "The FDA does not consider it appropriate to fortify snack foods such as carbonated beverages," the letter to Coca-Cola said, adding: "You should take prompt action to correct these violations".

It gave the firm 15 days to reply.

A Coca-Cola spokesperson told just-drinks today: "We take seriously the issues raised by the FDA in its letter. This does not involve any health or safety issues, and we believe the label on Diet Coke Plus complies with FDA's policies and regulations.

"We will provide a detailed response to the FDA in early January."