With medical marijuana legal in 23 states and Washington, D.C, there are now millions of card-carrying cannabis users working at companies across the U.S. But pot is still illegal under federal law, and many business owners still subscribe to the plant's Reefer Madness stigma and don't want to allow people to smoke on the job. For some of those owners, that can mean getting sued for failing to accommodate an employee who has a medical condition.

Regardless of how you feel about marijuana, there are certain rules employees and employers need to follow when it comes to drugs in the workplace. If you make a mistake, you could find yourself in court. Todd Wulffson, a partner at California-based employment and labor law firm Carothers DiSante & Freudenberger, is one of the many lawyers who have been busy defending employers in these types of cases. Wulffson says that to protect your business you need to update your employment policies and human resources programs, and train all managers.

First, you need to be familiar with the laws that have been passed in your state and consider a drug policy that doesn't prohibit employees from using cannabis on their own time. With 86 percent of Americans supporting medical marijuana, an overly restrictive policy may chase some of your workers to another employer. Marijuana, while still classified as a Schedule I drug without medical use, does have medical benefits, and a bipartisan bill to make medical marijuana legal on the federal level has been introduced in the Senate.

Until then, you need to take steps to avoid becoming a target of an employee lawsuit (whether the employee would have a strong case or not). "There are four scenarios that play out in these types of lawsuits that I see over and over again," Wulffson says. See the details below to find out what moves your company should make in each case.

1. Innocent inquiry

The first scenario is when an employee or an applicant innocently asks the question "'I just wanted to know, would you accommodate my use of medical marijuana?'" "That's a loaded question because you have to accommodate the underlying disability of the medical condition," Wulffson says. "But you don't have to accommodate being stoned at work."

If the query is put to the human resources department, the HR person should tell the employee that the company will accommodate his condition. At the same time, the employee should explain his condition, the treatment, and exactly what kind of accommodation he needs so you can have a dialogue about it. Where most companies falter is when a manager doesn't know the company policy and speaks out of turn.

"If an employee asks a line manager, they could easily say, 'Hell no! We don't accommodate stoners! You can't be stoned at work!'" Then the employee says, "Gee, I got glaucoma and I was hoping you'd accommodate my condition." If the manager doesn't tell the employee to go talk to HR and fires them, Wulffson warns, the result may be a lawsuit.

2. An ill employee stoned at work

The second scenario, Wulffson says, is when an employee with a serious disease is under the influence at work and gets called on the carpet: "The employee will say, 'I am getting treated for cancer and I am going through chemo. The only thing that helps is medical marijuana and I had to smoke a bowl at lunch to keep from throwing up. I am really sorry, I'll do something light until it wears off.'" Wulffson says that although you may have sympathy for the employee's situation, the only way to protect yourself from litigation is to institute a zero-tolerance policy for the use of any drugs, including medical marijuana, while at work.

Keep in mind, however, that if you are in a state that mandates employers accommodate medical marijuana (i.e., Arizona, Delaware, or Minnesota) you cannot fire a medical marijuana card-holding employee for a positive marijuana test. While it is indeed advisable to have a drug policy prohibiting marijuana use during work hours, you don't need to know about what employees are doing on their own time.

3. The future smoker

Wulffson says he's currently representing three clients who are in this situation: The employee comes to you and says she's suffering from anxiety or glaucom and needs to deal with the symptoms. She tells you she's about to go outside, walk 50 feet away from the building, smoke, and come back. "They're telling you they're going to do it, but they are not stoned right now, so you don't have the right to fire them right now," he says. "But, invariably, the manager says, 'No, no, no, no. Go home, stay home, you're fired.'"

Wulffson says you should not allow the employee to smoke while at work, but you can make allowances. Say something like this: "We will reasonably accommodate your condition, but we cannot allow you to be under the influence while on the clock--it's too risky for the company. You can go home for the rest of the day and come back tomorrow."

4. Social media smokers

Here, an employee goes on Facebook or Twitter and sees pictures of an applicant smoking a joint. The employee then emails the hiring manager to discourage him from hiring the person. When the candidate finds out you saw the photos, Wulffson says, "that's when they claim you didn't hire them because of either a perceived disability" and/or because you don't want to provide an accommodation for them.

You might find this is frivolous, but there are lawyers out there looking to cash in. "There is a cottage industry of lawyers that do nothing but bring claims related to medical marijuana against employers," Wulffson says. "Google 'medical marijuana rights' and you'll find 50 lawyers who write well-written letters about how you didn't accommodate the employee and you're getting sued for hundreds of millions of dollars, but today they'll take $15,000 to go away."

The takeaway

Wulffson says these lawsuits are catching a lot of employers off guard because of the confusion over medical marijuana laws. "It may be legal in many states, but it's still a federal crime," he says. California and other states will not prosecute someone with a medical card who is carrying less than a certain amount, but that's not a blanket permission. "You can't go on federal property, you can't work for a federal employer," he says. "'Don't work for a federal contractor because you could be fired and maybe jailed."

When it comes to drug use at work--whether it is an employee with cancer smoking marijuana or one popping Xanax to deal with anxiety--Wulffson suggests you should adopt a simple, straightforward company policy that reads something like this: "We don't allow the use of, the possession, or being under the influence of any illegal drug in the workplace. 'Illegal drug' is defined as 'the abuse of over-the-counter medication, prescription medication, medical marijuana, and alcohol."