This is something that is really a double edged sword...when you say a white student union you are classifying by nothing more than color of skin and not cultural heritage. If you were to say British student Union then it would be different.

Another problem with this is that you couldn't have an American student Union really because people of all nationalities are what make up this country and not just white people. and since there really isn't all that much history behind America (being a new country and all) there really isn't any cultural heritage to pass along except folk lore and music which has been a conglomeration from other cultures anyways.