Employment law - Under what circumstances is it legal, advisable

Questions for employment law

1) Under what circumstances is it legal, advisable, and/or ethical to engage in the following practices:
a) Require pre-offer medical examinations of some applicants and not others?
b) Require post-offer, pre-employment medical examinations of some applicants and not others?
c) Retain information generated by medical and pre-employment testing in each applicant's general personnel file?

2) Does the NLRB provide an appropriate mechanism for union action oversight? Why or why not?

3) Are the rights of white males protected under affirmative action? Why or why not?

4) Does affirmative action require meeting of quotas? Why or why not?

5) Is it appropriate to conduct a pre-employment physical? If so, when?

6) How can employers ensure that their performance evaluation process is non-discriminatory?