Drug testing, or perhaps more appropriately substance abuse testing, is a double-edged sword in the private sector. Not only can the employer be sued as the result of testing but he can be sued for not testing. Private employers find themselves in the classic "damned if you do, damned if you don't" situation. Large corporations are seen as deep pockets when matched against one of their employees and if the plaintiff's lawyer can find an issue and then get his or her case to the jury, corporate pockets can be very deep indeed. Hence, before examining the legal implications of testing, there is good reason to consider the legal implications of not testing.
Thomas H. Barnard, Legal Implications of Drug Testing in the Private Sector, 2 J.L. & Health 67 (1987-1988)