Drug testing has been a staple of the hiring process for decades, helping employers across industries to mitigate their risk in terms of cost, productivity, liability and employee well-being. This is unlikely to change anytime soon, particularly in automotive, construction, manufacturing and other sectors where safety is paramount.

But with more states working to decriminalize or legalize marijuana use, routine workplace drug screening deserves a closer look. Last summer, Quest Diagnostics reported that the number of American workers and job applicants testing positive for drugs reached a 14-year high, with positive screens for marijuana at the top of the pile.

What does this mean for employers?

The increased legalization—and utilization—of cannabis creates a decidedly gray area for employers. Companies need to re-examine their drug policies and potentially modify their approach when it comes to vetting job candidates.

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There are multiple factors to consider. First, in this era of low unemployment, attracting and retaining top-notch talent is a challenge—particularly in the legal market. When you make a negative marijuana drug test a requirement for employment, it has the potential to shrink the talent pool even further. This is especially true for companies in states with pro-cannabis legislation, but also impacts those in states where cannabis has not been legalized. If that company is hiring nationally, they're likely to see fewer candidates from legalized locations.