Basically, it’s legal in the United States if the practice reduces overall inequity. If the company were 100/0 split and at least two times larger in total workers than the 80/20 applicant pool, then they could hire exclusively from the 20% until they’ve reduced their split to 50/50.
(I am not your lawyer, this is not legal advice, I will not be providing citations.)
(I am not your lawyer, this is not legal advice, I will not be providing citations.)