WASHINGTON - Companies across the nation are facing issues concerning medical marijuana in the workplace, the Wall Street Journal reports.

A Michigan lawsuit against Walmart, where an employee who used medical marijuana was fired after failing a drug test, is of particular interest to corporate HR directors nationwide.

Fourteen states and the District of Columbia permit the use of medical marijuana by patients suffering from certain medical conditions, such as cancer or glaucoma. And the Obama administration has directed federal prosecutors to respect medical marijuana users who follow their states' laws, even if that conflicts with federal law, which bans marijuana use.

That conflict-of-laws scenario has created uncertainty for employers, who are trying to accommodate state laws on medical marijuana use while having to respect and enforce corporate drug-use policies that are based on federal law.

"It's certainly an issue that's coming up regularly," said Danielle Urban, an attorney with Fisher & Phillips. "Employers are between a rock and a hard place."

According to federal law, marijuana is listed as a Schedule 1 drug, and employers can fire or refuse to hire employees for using the drug without risk of violating the American with Disabilities Act or any federal anti-discrimination statute.

States vary in how they apply their laws. Courts in Oregon, California, Montana, and Washington have ruled that employers can rightfully fire medical marijuana patients for using the drug, while Rhode Island and Maine laws dictate that most employers cannot penalize individuals solely because of their use of medical marijuana.

Of considerable interest to employers is whether medical marijuana patients can use marijuana on-site or come to work impaired.

Michigan law forbids registered patients from facing disciplinary action at work because of their marijuana use, though it allows employers to terminate workers who use marijuana while on the job or who come to work high.

But determining if a worker is impaired on the job can be difficult if not expensive, requiring sophisticated instruments and testing.

Regardless of state laws that might permit medical marijuana use, some employers maintain that marijuana use leads to workplace accidents, raising safety concerns.

All eyes will therefore be on the Walmart suit, hoping that its resolution will shed clarity on an evolving legal issue.

A Walmart spokesperson labeled the decision to fire its employee as "difficult," adding, "As more states allow this treatment, employers are left without any guidelines except the federal standard. In these cases, until further guidance is available, we will always default to what we believe is the safest environment for our associates and customers."