I hope this message finds you well. I am a licensed attorney with over a decade of employment law
experience. It is a pleasure to assist you today.
As a matter of course, you do not necessarily have to have a drug testing policy in place as an employer to actually test your employees. The main issue here is that you cannot be discriminatory in how you test. The practice must be fair and impartial.
That said, and to the point of your question, you need to ask the test administrator to provide paperwork, if possible, as to their testing methods and what they do to insure that there are no false positives or mixed/tainted samples. Also, you need to ask them what, if any, appeal or re-test practices that they employ to insure accuracy and minimization of false positives. These are the two largest and most damaging issues for drug testing of employees.
So, the employer can take this action as long as it is not discriminatory (only testing men or only testing minorities). The issues above should be addressed with the administrator of the test.
Let me know if you have any other questions.
Best wishes going forward!