As an HR professional I would have to look at both sides objectively. Employees are allowed to partake in the use of marijuana recreationally but that does not mean that the employee may come to work under the influence of such a drug or coming into the workplace spelling like the drug. It is unprofessional to attend work in such a condition. I would also have to take a look at how often that employee was coming into work under the influence of the drug and how it was affecting their performance and reputation at work.

Considering the employer prohibits the use of any controlled substances or narcotics it would be wise that employees do not give the employer a reason to suspect that they partake in such things. Showing up to work under the influence of a substance the employer prohibits is not a good look. I must also ask if the employer has the employees take a drug test to maintain employment and assure themselves that substances that are prohibited are not being taken while on the job.

My response would be the same if the marijuana were for medicinal purposes. All employees should not be under the influence before or during the work day. That is something that they would have to partake in on their own time.