Jonathan Sigel quoted in "Employer's Guide to Drug Testing in the Workplace"02/17/2023
Because marijuana continues to be a Schedule I controlled substance at the federal level, employers have some leeway when testing for cannabis. While employers must still follow the drug-testing laws of the states of their employees, they can still test for marijuana use.
“Many employers have decided to treat marijuana as they do alcohol — only prohibiting the use of marijuana during the workday as well as forbidding employees from being under the influence of the drug at work,” said Jonathan Sigel, a partner at Mirick O’Connell in Massachusetts. “Employers (in high-risk industries) often choose to continue testing for marijuana for their safety-sensitive jobs because of the greater risk of potential harm that could be caused by an employee who is under the influence of marijuana at work.”
In other words, prohibiting controlled substances only while employees are at work is one way employers attempt to maintain safety standards while juggling new state legislation.