Regarding Drug and Alcohol Testing of Employees by Employers

Regarding drug and alcohol testing of employees by employers:

A) the NLRB makes it a mandatory subject of collective bargaining in a union setting.
B) the constitutional protection from unwarranted search and seizure protects private sector employees from the practice.
C) the Constitution prohibits any public sector employer from testing its employees under any circumstances without a warrant.
D) federal legislation sets forth comprehensive guidelines for the practice.