Let me see if I can guess what you're talking about. The following are items commonly bandied about on rightist talk-shows. So far as I know they are true, but - I really DON'T know. Ya know?
1. The founders of the UN were largely communists or fellow travellers, such as Alger Hiss.
2. The ACLU was explicitly founded by Communists as a Communist organization.
3. Anti-war groups such as ANSWER are closely related to communist and socialist groups.
4. In the early twentieth, Communists infiltrated anywhere they could. The NAACP, labor unions, the Screen Actors' Guild; even the NRA if they could get away with it. I have also read this in anti-Communist literature of the 1950s. That is, in one of J. Edgar Hoover's books on the subject. Speaking of the NAACP, some have said that Marxism was prevelant among educated Blacks in the early part of the last century. It is worth noting in this respect that Black-American free-market economist Thomas Sowell was a devotee of Marx in his early life, and read Das Kapital very thoroughly. (See his autobiography.)