Diesel Sweeties creator Rich Stevens posted a letter he received from LucasFilm Ltd requesting that he cease and desist (magic lawyer words) from selling several t-shirts that play off of Star Wars references (or at least might play off of Star Wars references). (Fleen posted a short comment on it.) Assuming arguendo (another favorite lawyer word) that Stevens is riffing off of Star Wars references in these t-shirts, so what? The questions are going to be about trademark, copyright and defenses such as fair use (including parody).
Unfortunately the reality is also that unless Stevens gets some pro bono (laywerly way of saying "free") assistance it's unlikely he's going to want to even get near the tar pit that would be litigation with a big corporation. I'm not sure what groups would be interested: CBLDF? EFF? Others? A good place to start might be The Chilling Effects website which is a useful guide to understanding your rights and the law related to these types of cease and desist letters.