They never sleep, gripe about overtime or quibble over paychecks. And -- with more than 5 million of them scattered around the nation -- they are ubiquitous.

From the top of Mount Fuji to the foyer of almost any city office and along nearly every road in between, the steady drone of vending machines is nearly inescapable.

But this army of mechanical vendors -- especially the humming band of beverage-selling ones -- have a darker, unacknowledged side, according to a Kanagawa Prefecture-based nongovernmental organization.

Behind their boxy facades, vending machines are an environmental scourge that is largely unrecognized, according to the Japan Association of Environment and Society for the 21st Century.

"Sure, vending machines are convenient. But they destroy city aesthetics and use massive amounts of energy resulting in the release of carbon dioxide," said Saburo Kato, head of JAES 21.

Cans and bottles from vending machines have a penchant for becoming roadside rubbish, he said, adding that the cooling agents in older machines gradually being taken out of service contain ozone-depleting gases that escape into the atmosphere if not properly disposed of. Newer versions, meanwhile, contain powerful greenhouse gases, he added.

After more than a year of discussion, surveys and debate, the group released a booklet in late 1999 that hits at the beverage vending machine industry as a creature comfort with little-realized negative sides.

More than 5 million vending machines are in operation throughout Japan. Just over 47 percent of them -- some 2.8 million -- sell beverages, according to Kazumitsu Matsuo, who is also a member of the NGO.

The term "vending machine," defined as "a machine (excluding telephones and entertainment machines, such as video games) that provides goods or services for money," covers a broad spectrum of devices, from train ticket machines and coin lockers to those selling stamps or erotic videos.

But it is beverage machines that are at the crux of the issue, the pair argue.

Sales from these lucrative machines topped those of convenience stores in 1997 and were four times that of coffee shops, according to the group's booklet, "Environmental Problems from the Perspective of Beverage Vending Machines."

While some vending machines are necessary, Kato and Matsuo contend that there is a glut.

The NGO calculates that beverage machines annually consume 7.8 billion kwh of electricity -- nearly the amount of energy generated in a year by a 1.1 million kwh nuclear plant, accounting for almost 1 percent of the nation's carbon dioxide emissions.

In recent years, the vending machine industry has developed more efficient "eco-vendor" machines that trim energy consumption by up to 15 percent.

"We have thought up various energy-saving measures. During July, August and September, the eco-vendor machines save energy by not cooling the cans from 1 to 4 p.m. This is the time during the day when demand is high and power companies need to supply energy, so we use more in the morning and less in the afternoon," said Takashi Kurosaki, a spokesman for the Japan Vending Machine Manufacturers Association.

The industry has also cut down on electricity consumption through the use of fluorescent lights and stronger insulation, he added.

However, Matsuo of the NGO maintained that these are merely an excuse to continue business as usual and avoid more drastic changes, adding that real change can be realized most effectively through municipal ordinances.

Although the total number of mechanical vendors in Japan is less than that in the United States, they are much more densely distributed. With an average of almost 15 vending machines -- nearly seven of them selling drinks -- crammed into each sq. kilometer, Japan boasts a vending machine concentration more than 20 times that of the U.S.

Kato and Matsuo claim a rethinking of the machines, the convenience they proffer and their place in society is needed and have a hunch that day may soon be at hand.

The city of Toyoda, Aichi Prefecture, has banned vending machines from public facilities, and many others have addressed the issue indirectly by passing ordinances prohibiting littering or encouraging cleanliness, Matsuo said.

"A surprising number of people have shown interest since we have taken up this issue," Kato said.

Partly in response to this interest and partly in the hope of inciting more, the group held a symposium at Tokyo's United Nations University earlier this year and plans to hold another one next month.

Still, no municipality has yet regulated the use of vending machines in both the public and private sphere.

As a reference for municipalities, the booklet offers a model ordinance. With a "goal of lessening the environmental burden of beverage vending machines and maintaining the city's scenery," the model draft would make the mayor responsible for regulating the placement, operating hours and product lineup of the machines.

"We are not calling for a ban on all machines, but a reduction," Kato said, adding that vending machines in some places -- hospitals and gymnasiums, for instance -- make sense.

"Vending machines are certainly convenient, but they clearly also have a big environmental impact. The big question is how to balance the two."