It is reasonable for employers to have the right to demand high performance levels at work.  It is not reasonable for employers to have any control over employees when they are not on the clock.  I have no personal stake in this since I have never consumed marijuana; however, liberty and personal freedom demand limits on the power of employers to control employee life when not being paid.  To get real about this matter, the drug test should be abandoned since it cannot tell whether the employee is impaired.  Instead, a performance test based on mental cognitive and motor skills could be employed to directly test for impairment.  Such a test could be completely computerized and take just a few minutes with the computer keeping a performance history of each employee and noting deviations from standard performance.  If the employee is found impaired, then the employer has a legitimate gripe.