When states first began legalizing medical marijuana in the mid-to late 1990s, not many people would have guessed that in fewerthan 20 years, the substance would be decriminalized in 16 states,fully legal for adult use in two and approved for medical use in22.

There's a lot of overlap among those states, but between thestates with decriminalization statutes on the books and those thathave legalized marijuana for medical use, more than half of thestates in the country have enacted laws that somewhat or fullyprotect adults who use marijuana.

With this political sea change have come new challenges, notjust for dispensary owners and marijuana advocates, but foreveryone who owns a business in those states. Until the federal lawis changed, employers in states that allow some form of marijuanause are caught in the unique legal limbo that's created when statelaw allows something and federal law prohibits it.

Only four states—Arizona, Delaware, Minnesota and RhodeIsland—provide any level of legal protection for employees who areprescribed medical marijuana, and Arizona and Minnesota's lawsoffer the strongest protections for employees. The question ofmarijuana legalization (medical or otherwise) has forced manybusiness-owners to examine their policies and make decisions abouthow they will communicate with their employees about thosepolicies.

And unless there's a safety issue involved (a position thatrequires operating heavy machinery or driving, for example), manyhuman relations legal experts suggest thinking carefully beforeplacing a blanket ban on employee medical marijuana use.

Valerie Samuels, an attorney with Posternak Blankstein &Lund LLP in Boston and co-chair of the firm's employment law group,says employees can petition to have their medical marijuana useaccommodated under the Americans with Disabilities Act—but thatdoesn't mean employers must comply.

“You cannot force an employer to accommodate an illegalactivity, and marijuana remains illegal under federal law,” shepoints out. “As long as it's illegal under federal law, employerswon't have to accommodate it. And under federal law, if an employeeis fired for having marijuana in his or her system, the employeewould have no recourse.”

Danielle Urban, a partner at Fisher & Phillips in Denver,has become an expert on pot-related employment questions. Coloradois one of two states, along with Washington, that legalized pot forrecreational use back in the fall.

“Although marijuana use is not protected under the ADA,” sheexplains, “if someone comes to you and says they have adebilitating medical condition, you can't just say, 'Well, we'renot going to accommodate marijuana use,' without looking at otherpossible accommodations. It would be unwise to end the conversationwithout exploring any other solutions to their condition. And in astate like Arizona, you may have no choice but to incorporatemarijuana use unless it's in a safety position.”

One of the biggest problems for employers when it comes tomarijuana is that, unlike alcohol, there's no way to gaugeimpairment through a scientific test; daily marijuana users—whichmany medical users are—will have a much higher tolerance for theactive chemicals in marijuana than will those who only use itoccasionally.

“In Colorado, a lot of employers don't want to say to theiremployees, 'You can't use it even on your own time,'” Urban notes.“They don't want to be involved in their employees' personallives—and probably some of the employers voted for the Amendment.But there's no easily accessible way to test impairment, soemployers often still have zero-tolerance policies. Because the lawis still so gray, if someone hurts someone else at work and theytest positive for marijuana, the burden is going to be to show thatthey weren't impaired—and that is difficult to do. Employers maywant to have a philosophy of permitting employees to do what theywant on their personal time, but the current testing technologymakes that difficult.”

Samuels says employers should have a clear policy aboutincorporating disabilities in the workplace.

“They should include in their policy that they're not going toaccommodate anything that's a health and safety violation or that'sunlawful. But if an employer called me and said, 'I have anemployee who uses medical marijuana, and he's a good employee, andI want to keep him,' then I would say if the employer wants toaccommodate that and is comfortable with it, that's fine.”

All in all, communication between employers and employees iskey, experts say.

“It's a good idea to tell your employees how you're going tohandle the issue,” Urban says. “Employees in states like Coloradoand Washington are shocked to learn that they could lose their jobsfor testing positive. So it's a good idea to tell your employees,'By the way, this is our policy. You'll be tested for these reasonson these occasions, and if you test positive, this is what willhappen.'

“I think in states where medical marijuana is permitted,employees think that having the card means they can use it withimpunity, but that's not the case. It's better to avoid that—anddon't surprise your employee,” she says.