After the fact union charges

Hello,

I recently was fired from my job at AT&T, on 12/14/2012, during my employment there was a 2-day strike by the CWA union, I exercised my NLRA right and chose not to participate in the strike, I crossed the picket line and went to work. This was in August of 2012. About 2-3 days after I was fired from AT&T, I received a certified letter from the union saying they were bringing charges against me for crossing the picket line, and that I was to appear before them on trial. They are not going through the state or local courts, but basically a kangaroo court of their own. I am choosing to not come to this "trial" and appear before them. Isn't what they are attempting to do here a violation of the NLRA and also my right to non-participation? If yes, How do I file a charge against them? I have been doing some research and discovered that the union was supposed to tell me that I could become a "dues paying non-member", or I had the right to resign my membership. This was NEVER communicated to me, and now AFTER I've been fired, they are trying to charge me and possibly fine me? Also what can happen if I do not attend their "hearing"?