"We're actively investigating these companies and their products," Connecticut Attorney General Richard Blumenthal told USA Today in a story published Monday.
Public health officials in California, Oregon, New Hampshire and New Jersey said the smokeless devices are the latest thing in the tobacco wars and could be used to circumvent smoking bans.
E-cigarettes, as they are commonly called, are used by at least a half-million U.S. residents, said Matt Salmon, who heads the Electronic Cigarette Association.
"People who smoke ought to have better alternatives, because some can't quit," said Salmon, whose father, a longtime smoker, recently died of cancer and emphysema.
E-cigarette distributors filed lawsuit against the U.S. Food and Drug Administration after the agency said e-cigarettes it tested contained carcinogens.
"It's a new frontier. We don't know what the dangers are," said John Banzhaf, a spokesman for Action on Smoking and Health, an anti-smoking group.