The state’s new medical marijuana law will force hard choices on employers and workers — forcing some to fire medicinal pot users while others will have to make tough calls on whether employees’ drug use is interfering with their work.

Public safety employers such as the Boston Fire Department say it won’t tolerate pot use, even as ?medication.

“Boston Fire does conduct random drug and alcohol testing of its uniform force,” spokesman Steve MacDonald said. “Marijuana use is not allowed.”

Meanwhile, Associated Industries of Massachusetts is advising businesses not to fire employees just for using medical marijuana, even if they fail drug tests — unless they come to work stoned.

“The bottom line for the employer is that people cannot be impaired in the workplace,” AIM spokesman Chris Geehern said. “If an employer becomes aware an employee is using medical marijuana, that in and of itself is not grounds for taking any action. The break comes when that employee appears to be impaired in the workplace.”

Massachusetts and 19 other states allow people with a range of medical conditions to use different forms of marijuana as treatment, but pot remains illegal under federal law. Signs of drug use in public transit workers, truckers and commercial pilots who are tested following accidents might also lead to their ?termination.

“If you’re covered by federal DOT drug testing, that’s what holds,” Geehern said.

Kabrina Krebel Chang, an employment law expert at Boston University’s School of Management, said even with the Bay State’s new medical marijuana law, employers maintain the right to fire a worker for failing a drug test.

“If you’re an employee who medicates with marijuana, there are very few laws that protect you if you fail your company’s drug tests,” she said.

Employers, she added, are reluctant to make exceptions to drug policies and won’t want to be responsible for checking whether their workers have authorization to use marijuana.

Partners HealthCare, the largest private employer in Massachusetts, with 60,000 workers, has not yet decided how to deal with the issue of medical marijuana use among employees, said spokesman Rich Copp.

“Partners HealthCare, like many other employers, is in the early stages of evaluating what changes may need to be made to existing HR policies. Any revisions to our policies will be made guided by appropriate statutes and with the best interests of our patients and our employees in mind,” Copp said.

Geehern said, “We’re urging employers to take this on a case-by-case basis. This is all new. They should look at each case separately rather than blindly apply ?a policy.”