Since when...? Do you have something to verify that the "federal government" actually requires any business to perform a drug test...?
I'm not sure what business you're in, but I'd like to know if this is actually true or not...I did some searching and I couldn't find anything to confirm it, beyond government employees and professional athletics.
Well z, to find every case where it's applicable would surely be a daunting task. I believe it's included the the massive collection called the "Code of Federal Regulations". For example:
Subtitle A--Office of the Secretary of Transportation
PART 40_PROCEDURES FOR TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING
TITLE 14--AERONAUTICS AND SPACE
CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
PART 121_OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL OPERATIONS--Table of Contents
Subpart AA_Continued Airworthiness and Safety Improvements
Sec. Appendix I to Part 121--Drug Testing Program
Workers in the nuclear industry must also submit to random drug screenings as a condition of employment. This is made known to every employee and contractor who performs work at a nuclear generating station. Not to mention background checks, fingerprinting, and credit checks.