Graphic novels are a relatively new literary medium, and it's vitally important to make sure public libraries are not restricted from offering them.
I looked for organizations working on this issue. Comic Book Legal Defense Fund is positioned to do so, but they haven't focused on libraries in the past, as far as I know (sadly, their news page has a lot more to say about all the fundraisers and parties they are having than about what they are actually doing with all the funds). The American Library Association has a large section of their web site devoted to Advocacy issues, which includes pages entitled Intellectual Freedom Basics and What You Can Do to Oppose Censorship.
You can join the ALA as an associate member, which includes the opportunity to join an Intellectual Freedom special interest group.