A divided federal appeals court is upholding a President Barack Obama-era regulation that barred e-cigarette smoking—also known as vaping—on both inbound and outbound US flights.

The US Department of Transportation officially banned electronic cigarettes on flights in March of 2016 to clear up any confusion as to whether they were also outlawed like traditional tobacco cigarettes.

The Competitive Enterprise Institute and the Consumer Advocates for Smoke-Free Alternatives sued, alleging Congress' "no smoking" statute didn't apply to e-cigarettes.

"Today’s court ruling creates a dangerous new rule for interpreting the law," Sam Kazman, the institute's general counsel, said in a statement about the decision from the US Court of Appeals for the District of Columbia Circuit. "It allows the commonly understood language of Congress's 30-year-old no-smoking statute to be stretched in a ban on e-cigarettes—even though e-cigarettes involve no combustion and produce no smoke."

There are plenty of studies out there on the health consequences of vaping, though that work is in its early stages compared to scientific knowledge on cigarettes. Regardless, the three-judge court, ruling 2-1, said vaping should be banned because scientists are only beginning to understand the health consequences for those vaporizing and for people around them.

"We must ask whether the term 'smoking,' in a statute enacted before modern e-cigarettes existed, covers these devices," US Circuit Judge A. Raymond Randolph wrote (PDF) for the majority.

Randolph answered his own question in the affirmative. The lone dissenter, Judge Douglas Ginsburg, said he wasn't sure vaping counted as smoking.

"True, e-cigarettes might fit within these definitions if one squints hard enough, but as the court itself notes, ‘we cannot just tally the dictionary definitions,’" Ginsburg wrote.

When announcing the ban last year, the transportation agency said: "This final rule is important because it protects airline passengers from unwanted exposure to aerosol fumes that occur when electronic cigarettes are used onboard airplanes. The Department took a practical approach to eliminate any confusion between tobacco cigarettes and e-cigarettes by applying the same restrictions to both."

A study Ars reported on last year showed an unexpected health effect unique to vaporizing. After comparing genetic information swabbed from the noses of smokers, vapers, and non-users of both, researchers found that smoking suppresses the activity of 53 genes involved in the immune system. Vaping also suppressed those 53 immune genes—along with 305 others. The results were presented at the annual conference of the American Association for the Advancement of Science in Washington.

British health officials, meanwhile, said that e-cigarettes are 95 percent less harmful than tobacco cigarettes.

There are a variety of e-cigarette styles. One type has a powered atomizer that is activated upon inhalation. Other types use a heating coil that is switched on by the user. In all the devices, liquid nicotine or other products in a cartridge are heated, become vapor, and are inhaled. Nicotine content varies by product and maker. The devices can also be used to smoke marijuana oil.