Hmm? There are laws against some forms of discrimination, but organizations have freedom of association just as individuals do. For example, political affiliation is not a protected class, so (in some states and some contexts) it is perfectly legal for a private company to decline to hire someone on the basis of their political views.
No they don't, there are laws against that, for example you can't decide to ostracize black people from your company, you will get sued for that.