Puffing on electronic cigarettes is already a no-no on flights, but the government wants there to be no doubt.

The Department of Transportation is proposing to explicitly ban the use of the devices on planes.

"Airline passengers have rights, and this new rule would enhance passenger comfort and reduce any confusion surrounding the use of electronic cigarettes in flight," said Transportation Secretary Ray LaHood.

Electronic cigarettes look like the real thing, but they're actually battery-operated devices that turn nicotine into a vapor that is inhaled by the user, according to the FDA

They're a potential cause for concern because "there is a lack of scientific data and knowledge of the ingredients in electronic cigarettes," the DOT said.

But the Tobacco Vapor Electronic Cigarette Association criticized the move, insisting that the devices only emit water vapor.

"It makes absolutely zero sense," said Ray Story, the group's CEO.

"It only gives the smoker a dosage of nicotine, but it doesn't do anything else to the innocent bystander. ... I have sat next to people who wore a particular type of cologne that was far more intrusive than what this particular product is."

The DOT believes its current ban on smoking of tobacco products is broad enough to include electronic cigarettes, but wants to eliminate any confusion.

Some airline passengers have been "vaping" on planes, convinced that the devices are exempt from the ban.

In July, a Sandy, Utah, man was arrested after an altercation that began when he started using an electronic cigarette on board a Southwest Airlines flight from Los Angeles to Salt Lake City.

The story prompted hundreds of comments from CNN.com readers, many defending electronic cigarettes and arguing they're a smoke-free way to provide relief for passengers suffering from nicotine withdrawals during a flight.

"The problem is not with the people using this device, but with the people around them who are psychologically affected by the fact that it LOOKS like a cigarette and someone is sucking on it," one commenter wrote.

But others worried about the safety of using the devices at 35,000 feet, as well as their health effects on others.

"I sat next to someone who was e-smoking and it's impossible to contain all of the nicotine mist. I don't want to breathe that stuff and shouldn't have to sit next to someone on a plane who is spewing chemically loaded mist. Get a patch or nicotine gum if your addiction is that bad," a commenter wrote.

The DOT's proposed rule would apply to all U.S. and foreign airlines on scheduled flights to and from the United States. Officials are also considering whether to extend the ban on smoking to charter flights.

Amtrak has already banned the use of e-cigarettes on trains and in any area where smoking is prohibited, the DOT said, and the U.S. Navy doesn't allow them below decks in submarines.