The Center for Science in the Public Interest (CSPI) said it would sue both firms if they did not stop making the claim on Enviga, a green tea-based energy drink set for official launch in January.
The announcement coincided with a US Food & Drug Administration (FDA) hearing on how to regulate labelling and health claims for functional foods and beverages, such as Enviga, which have no legal category of their own to date.
It is the optimum combination of Enviga's green tea, caffeine and plant micronutrient content which creates the 'negative calorie effect', according to chief Coca-Cola scientist Rhona Applebaum.
The formula was made possible through access to decades of research on green tea by the Nestlé Research Center in Switzerland. It found the tea contained a powerful antioxidant, EGCG (epigallocatechin gallate), which could speed up metabolism and energy use when combined with caffeine.
Tests have shown that drinking three cans of Enviga everyday could burn an extra 60-100 calories in thin to normal weight people, the firms announced.
CSPI accused both companies of misleading advertising, alleging that evidence for Enviga's 'negative calorie' effect was not substantial.
It also criticised the drink's caffeine content, around 300g in one can, which sits right at the top end of the maximum daily intake advised by the American Dietetic Association. The same limit is advised in the UK by the country's Food Standards Agency.
Some scientists in the US recently called for all caffeinated drinks to show caffeine content on their labels, even carbonated sodas. Current caffeine levels in drinks were not clear enough for consumers, their article, published in the Journal of Analytical Toxicology, said.
"In certain people, consumption of caffeine causes serious health effects, such as anxiety, palpitations, irritability, difficulty sleeping and stomach complaints," said Dr Bruce Goldberger, one of the researchers.