Call them e-cigarettes, vapes, e-juices or e-liquids. Just don’t call them tobacco.

Early last Thursday, Missouri legislators overwhelmingly overrode the governor’s veto of a bill governing electronic cigarettes and the nicotine-infused mixtures they deliver. While the new law bans sales to minors, it also prevents e-cigarettes from being classified as "tobacco products."

“It was operating under the guise of protecting youth, but really it just created a special carve-out for a special interest,” says Traci Kennedy, executive director of Tobacco-Free Missouri.

Tobacco-Free Missouri opposed the law, along with the American Cancer Society, the American Heart Association and other health groups.

While the law doesn’t plainly forbid regulation of e-cigarettes, these groups point out that, by defining e-cigarettes as not tobacco, it keeps them from being subject to the same taxes and health-requirements as traditional cigarettes.

A.J. Moll, on the other hand, celebrated the law’s final approval.

“This new law sends the message that Missouri is not for sale to heavily-funded special interest health groups," says Moll, vice president of media relations for the Bistate Regional Advocates for Vaping Education, which operates in Illinois and Missouri.

Moll's group, along with many e-cigarette retailers, support the law and its ban on sales to minors. He says it’s too soon for additional regulations because not enough is known about the health effects of e-cigarettes.

But while the debate in Missouri seems to be settled, there’s a big cloud forming on the e-cigarette horizon.

The Food and Drug Administration is considering a rule that would take a very different approach to e-cigarettes. In contrast to Missouri’s new law, the agency is considering classifying e-cigarettes as tobacco products and regulating them as such. That would mean e-cigarette makers would have to post health warnings and disclose ingredients.

“There could be a potential conflict if the federal government wants to regulate e-cigarette products in one way and Missouri wants to do it in another, says Allen Rostron, a law professor at the University of Missouri -Kansas City.

“To the extent that that sort of conflict does arise, the federal law is going to prevail over the state one. The U.S. Constitution has a clause in it known as the Supremacy Clause that says that federal law is the supreme law of the land," Rostron says.

Missouri’s e-cigarette law isn’t the only such law that would run counter to the proposed FDA rule. According to the American Cancer Society, over half the states have passed laws banning sales to minors but preventing tobacco-style regulation.

E-cigarette advocates call the FDA proposal an overreach, although many health advocates like Kennedy say it still doesn’t go far enough to protect children and consumers.

“What’s really a key thing that’s missing is there’s no sales or marketing restrictions on e-cigarettes," Kennedy says. "So things like celebrity endorsements and television ads and things that really appeal to youth aren’t a part of this current rule.”

The FDA has not said when it will decide whether to adopt the proposed rule.