For those who need to search, that seems to roughly translate to "declaration of non-compatibility". CCC had declared that members of far-right groups are not welcome.

I don't think the KKK are a very good analogy for this; a better example might be McCarthyists/the House Committee on Un-American Activities, since they attack people based on political affiliation, which is at least nominally chosen, rather than inborn characteristics like skin color. Also the KKK made much more use of direct physical violence, rather than social and legal violence.