I am confused by the question. Another company in the same "system" as the current employer had an employee take a drug test and the person failed? There is not an automatic right to privacy in whether the person is using illegal drugs or not. If they are using prescription drugs for a medical disorder, like taking benzodiazepines for anxiety is another issue entirely. So, more facts are needed. You would be best served wit talking to an employment attorney in person to go over the facts and exactly how this panned out. Avvo has a great Find a Lawyer tool
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.