If you’re a small-business owner and marijuana has been legalized in your state, should you care?

The short answer is, yes. Nearly half of small businesses don’t have a policy about cannabis use in the workplace and 10% have had employees show up under the influence of a controlled substance at work, according to a survey released Wednesday by Employers Holdings, a workers’ compensation carrier.

The study polled 501 businesses nationwide that employed fewer than 100 employees, in states with varying legalization laws.

Twenty-three states have legalized medical marijuana and four states and the District of Columbia have legalized recreational cannabis.

A wide majority of respondents — 81% — said they were “unconcerned” about employees coming to work under the influence, but in states that have legalized marijuana use, a lack of policy could lead to major legal headaches.

“All employers regardless of size should have a drug and alcohol policy,” says Todd Wulffson, an attorney at Carothers DiSante & Freudenberger who represents employers. Wulffson says that if an incident involving marijuana happens in the workplace, the Occupational Safety and Health Administration, which is a federal agency, is likely to step in, and the federal illegal status of the drug will trump state law. [Read more at MarketWatch]