Section 4 of Chapter 151B of the General Laws is hereby amended by adding after subsection 19, the following subsection:-

20. For an employer or his agent, because of the presence of tetrahydrocannabinol or marijuana metabolite in the blood, urine or other body sample provided by the individual, to refuse to hire or employ or to bar or to discharge from employment such person or to discriminate against such person in compensation or in terms, conditions or privileges of employment, unless based upon probable cause to believe that the person is impaired at work by reason of cannabis consumption and has caused or is at imminent risk to cause harm to a fellow employee, customer or the public due to such impairment.

It shall be a defense to such employment action if the employee, due to the presence of tetrahydrocannabinol or marijuana metabolite in the blood, urine or other body sample provided by the individual, is unable to maintain licenses, credentials, or other qualifications that are reasonably necessary for the performance of the employee’s position, regardless of whether such licensing, credentialing, or other qualifications prohibit the employee from using marijuana. Nothing in this section shall be deemed to interfere with or preempt any rights or obligations of an employer under federal law or regulation.