Is there any rules barring a white person to join a historically black Greek organization?

So on my campus there are a lot of choices in Greek life. I was thinking about rushing but when I tried to look into some "black" fraternities (as they are called on campus) I was not only turned down but might as well have been shunned. Is this common? Is there some rule that says I can't join? At the risk of this becoming an issue I refuse to admit what school I'm from or the frat in question so please don't ask. But I do want to know, am I barred from trying & if not what are my chances if I try?