Consider this your St. Patrick's Day public service announcement: Gathering together for a round of green happy-hour beers can be a good way to nurture your business culture--and maybe even make you smarter, according to recent studies. But cocktails and colleagues don't always mix. Not only can the pairing lead to unwanted romantic overtures, employers can easily become embroiled in liability claims and lawsuits. 

Of course, you wouldn't be alone in endorsing alcohol at work. Twitter welcomes all new employees with a swag bag that includes a bottle of wine, company reps told QuartzOpower, an energy data company based in Arlington, Virginia, gives every new hire a bottle of Veuve Clicquot champagne. Manchester, New Hampshire-based internet-performance company Dyn takes boozey business a step further, with beer on tap in its office kitchen, according to Business NH Magazine. And in perhaps the clearest display of Mad Men-inspired culture: Adzerk, an advertising-technology company, has its own office Scotch collection. 

Thus far, Adzerk says it hasn't run into any problems related to happy hour: "Our core value is that we're all adults," CEO James Avery told Inc. Opower, for its part, also reports not having experienced any issues related to happy hour, but other celebratory occasions involving alcohol have been problematic for the company: "We had some predictable wildness around our IPO," according to a spokesman, who refused to offer any details. Still, the company clings to its "behave like a grown-up" policy when it comes to policing participants.

No matter how fun your company culture may be--or how much faith you place in your workers--happy hours run amok can pose legal issues. "Even if the event is held after hours, and off company property, it's still a company party and all the rules apply," says human resources specialist and Inc. columnist Suzanne Lucas. That means that if a higher up makes a pass at an intern, it's still considered sexual harassment. George Vallas, an employment attorney at The Ottinger Firm, adds: "The biggest issue that we see with holiday parties is liability for anti-harassment or anti-discrimination lawsuits." Hostile work environment claims are particularly common among small businesses, notes Vallas.

More pressing still are the liabilities that you could incur for an employee's behavior after the event: An anonymous respondent told Business NH Magazine, for instance, that her company stopped allowing Friday afternoon happy hours when an inebriated employee got into a car accident on his way home from work. That's also grounds for a workers' compensation claim, Vallas says, which can end up being "devastatingly expensive" for the employer. 

Here are three ways to avoid triggering your own cautionary happy-hour tales: 

1. Make sure that everyone feels included.

Once you've checked that all drinkers are 21 or older--and you can have HR run a list to confirm this--extend the invite to all personnel, even those who are 40 or older, Lucas advises.

2. Don't punish employees for not attending.

There are plenty of reasons that people might not want to attend a company happy hour. Lucas notes just a few: Employees may be recovering alcoholics, they may practice a religion that doesn't allow drinking, or maybe they just don't like being around others who are drinking.

So don't think an employee isn't a team player just because she decides to opt out.    

3. Set limits on how much people can drink.

Lucas also urges owners and managers to consider limiting employees to a single drink, tempting though it may be to keep an open tab. And perhaps most importantly, you should be clear about what you expect from your employees ahead of time. In other words, let the green beers floweth--to a point.