"Indeed, it's been a way of life for him—much
as it was for his late father, Leo Penn, an actor and
director who was blacklisted as a communist when
he refused to name names before the House Un-
American Activities Committee more than six decades
ago.
In the early 2000s, Sean Penn was a supporter of Not
In Our Name (NION), a self-described "peace"
movement established by the Revolutionary
Communist Party . NION was famous for its "Pledge
..."
http://www.frontpagemag.com/fpm/261458/sean-penns-el-chapo-odyssey-discover-networks