The United States government makes many rules which cover all aspects of employment, The first set of rules are related to discrimination.
First, the Americans With Disabilities Act specifies that you cannot refuse to hire someone for a position if they are capable of doing the job with reasonable accommodation. In the case of a waitress, there are certain physical requirements for the job that might limit certain physically challenged people.
Next, you cannot discriminate in terms of race or religion. For example, you could not refuse to hire a black woman on the basis of race, and if you hired an Islamic woman, she would need to be allowed to wear a hijab; and Islamic men would need brief breaks for required daily prayer.
Descriminating on the basis of age and appearance are also illegal except where there are legitimate occunpational qualifications.