The rules will apply to about 10,800 companies that operate 20 or more machines.
Nearly three quarters of those companies have three or fewer employees, and their profit margin is extremely low, according to the National Automatic Merchandising Association.
An initial investment of $2,400 plus $2,200 in annual costs is a lot of money for a small company that only clears a few thousand dollars a year, said Eric Dell, the group's vice president for government affairs.
"The money that would be spent to comply with this — there's no return on the investment," he said.
While the proposed rules would give companies a year to comply, the industry group has suggested a two-year deadline and is urging the government to allow as much flexibility as possible in implementing the rules.
Some companies may use electronic displays to post calorie counts while others may opt for signs stuck to the machines.
The FDA also is working on final rules for requiring restaurant chains with more than 20 locations to post calories information, something some cities already mandate and some large fast-food operations have begun doing voluntarily.
A 2011 study in New York found that only one in six customers looked at the information, but those who did generally ordered about 100 fewer calories. A more recent study in Philadelphia found no difference in calories purchased after the city's labeling law took effect.
"There is probably a subset of people for whom this information works, who report using it to purchase fewer calories, but what we're not seeing though is a change at an overall population level in the number of calories consumed," said Brian Ebel, the study's author and an assistant professor at New York University's department of population health and medicine.
Ebel said he wouldn't be surprised if the vending machine labels end up being equally ineffective, but he said it's possible that consumers might pay more attention to them for a couple of reasons.
In some locations, a vending machine might be the only food option, he said.
And reading a list of calorie counts on a machine will be less overwhelming than scanning a large menu at a fast-food restaurant with other customers waiting in line behind you, he said.
"It could go either way, but I think there's at least some reason to think it could be slightly more influential in vending machines."
Even without the calorie counts, consumers already have ways to make healthier choices from vending machines.
The vending machine industry group launched its "Fit Pick" system in 2005, which includes stickers placed in front of products that meet healthy guidelines for fat and sugar content.
The program is used by nearly 14,000 businesses, schools and government agencies, as well as all branches of the military.