This November, voters in Richmond, Calif., will also decide whether to approve a penny-per-ounce tax on sugary drinks.
The decision to post calorie information follows the Supreme Court's decision this summer to uphold President Obama's health-care overhaul, which includes a regulation that would require restaurant chains and with more than 20 locations and vending operators with more than 20 machines to post calorie information.
McDonald's Corp. also announced last month that it would begin posting calorie information on its menus nationwide. Like the soda industry, the fast-food giant said it was a voluntary decision and not spurred by the pending requirement.
In addition to public health concerns, soft drink makers are dealing with shifting consumer habits. Soda consumption per person has been declining in the U.S. since 1998, according to the Beverage Digest. The decline is partly the result of the growing number of options such as flavored waters, bottled teas and sports drinks -- which Coke, Pepsi and Dr Pepper also make.
As a result, Coke, Pepsi and Dr Pepper are focusing on developing more diet drinks, as well as expanding into other drinks to reduce their reliance on sodas.
There is no timetable for when all vending machines will be converted. Coke, Pepsi and Dr Pepper often work with third-party operators to provide drinks in vending machines; Neely said the companies will work with those outside operators to convert all machines over time.
Vending machines account for about 13 percent of sales volume, a figure that has remained relatively unchanged in recent years, according to Beverage Digest.
Soda consumption is often identified for playing a role in rising obesity rates, although other factors such as a lack of physical activity and overeating also contribute.
In September, the New England Journal of Medicine published a decades-long study of more than 33,000 Americans that showed sugary beverages interact with genes that affect weight, meaning they are especially harmful to people who are hereditarily predisposed to weight gain.
Bonnie Sashin, a communications director for a nonprofit organization in Brookline, Mass., says she stays away from sugary drinks, limiting herself to a can of Diet Dr Pepper or Diet Coke about twice a month. But she thought the move to display calorie information on vending machines was a positive development.
"Anything that helps us be more educated about calories is a good thing," Sashin said.