Employers in the eight states that approved marijuana-related initiatives on Tuesday should set up written rules and procedures now to deal with the issue if they have not already done so, experts recommend.

Recreational marijuana use was approved in California, Massachusetts, Maine and Nevada, with only Arizona voting the measure down, according to Washington, D.C. -based group NRML, which advocates marijuana’s legalization.

Medical marijuana-related initiatives were approved in Arkansas, Florida, Montana and North Dakota.

There should be “a measured and cautious reaction” by employers, said Tad A. Devlin, a partner with Kaufman Dolowich & Voluck L.L.P. in San Francisco.

Employers should establish policies and procedures now to address the issue. “It’s going to be a necessary component of employee handbooks,” said Mr. Devlin. 

Employee training will be “critically important” as well, said Mr. Devlin. “I would recommend it be part of mandatory training for managers, rank and file and executives, so it’s a top down, bottom up understanding of how the company does business.”

With respect to medical marijuana, “There’s a tendency among employees to believe if they have a medical marijuana card that they’re entitled to use it, and they’re not thinking they can lose their job for testing positive,” said Danielle S. Urban, a partner with Fisher & Phillips L.L.P. in Denver. 

But, “You are still free to have a zero-tolerance policy,” she said. “You are probably still OK to say, ‘If you test positive, we’re not going to hire you or will fire you,’” even if the medical marijuana’s use has been approved, Ms. Urban said.

Employers may want to consider, however, if they necessarily want a zero-tolerance policy in businesses where safety or federal law is not an issue, experts say. 

“If you’re an employer that needs to hire young people,” such as in the technology or the graphics design industry, “you need to be realistic about your workforce, and if you’re going to be hiring lots of 23-year-old computer programmers and coders, then you have to decide whether you want take a rule that’s going to make it hard to hire 23-year-old coders,” said Hanan B. Kolko, a member of law firm Meyer, Suozzi, English & Klein P.C. in New York.

Meanwhile, marijuana use remains prohibited under federal law, and employers in heavily regulated industries such as transportation, as well as those where safety is an issue, must still have a zero-tolerance policy, experts say.