Actually it might be illegal. Read below regarding recruitment.

https://www.eeoc.gov/laws/practices/

Recruitment

It is also illegal for an employer to recruit new employees in a way that discriminates against them because of their race, color, religion, sex (including gender identity, sexual orientation, and pregnancy), national origin, age (40 or older), disability or genetic information.

For example, an employer's reliance on word-of-mouth recruitment by its mostly Hispanic work force may violate the law if the result is that almost all new hires are Hispanic.