The reasons given: sexually explicit material, it is unsuited to the age group and it has violence.
Careful about the spoilers below:
Read more: http://www.care2.com/causes/banned-books-the-hunger-games.html#ixzz1telLsWBY
http://www.blogher.com/banned-books-week-suzanne-collins-hunger-games
Ummm, I read all three books and didn't see ANY sexually explicit material. But maybe the sex was hidden in camouflage. Or maybe a kiss is considered sexually explicit. Ummm... confused at that. As for the "it has violence" -- ummm, DUH! Unsuited to the age group -- that depends on the child. My oldest has read it and seen the film. No, not thirteen yet. LOVED it. Loved all three.