Coca-Cola and PepsiCo are changing the way they make the caramel colouring used in their drinks as a result of a California law that rules drinks containing a certain level of carcinogens must bear a cancer warning label.
The companies said the changes will be expanded across the US to streamline their manufacturing processes. The changes have already been made for drinks sold in California.
Coca-Cola and PepsiCo account for almost 90% of the US soft drink market, according to industry tracker Beverage Digest.
The American Beverage Association, which represents the broader industry, said its member companies will continue to use caramel colouring in certain products but that adjustments would be made to meet California's new standard.
"Consumers will notice no difference in our products and have no reason at all for any health concerns," the association said in a statement.
A representative for Coca-Cola, Diana Garza-Ciarlante, said the company had directed its caramel suppliers to modify their manufacturing processes to reduce the levels of the chemical 4-methylimidazole, which can be formed during the cooking process and as a result may be found in trace amounts in many foods.
"While we believe that there is no public health risk that justifies any such change, we did ask our caramel suppliers to take this step so that our products would not be subject to the requirement of a scientifically unfounded warning," Ms Garza-Giarlante said in an email.
The Centre for Science in the Public Interest, a consumer advocacy group, filed a petition in February with the US Food and Drug Administration to ban the use of ammonia-sulphite caramel colouring, which is now being reviewed.
A spokesman for the Food and Drug Administration said a consumer would have to drink more than 1,000 cans of cola a day to reach the doses administered that have shown links to cancer in rodents.
The American Beverage Association noted that California added the colouring to its list of carcinogens with no studies showing that it causes cancer in humans. It noted that the listing was based on a single study in lab mice and rats.