Drug tests are searches without warrants
Drug testing violates the foundation of American law, which is the presumption of innocence until proven guilty. There is also little if any evidence that they do what they are intended to do.
Most people would not let the police search their home, or even their car, without a reason being given, and maybe not without a warrant. Why then do we as a society allow employers to search our physical bodies without any cause at all, much less having a warrant to do so.