There is no official procedure, or protocol. Since all libraries are free to choose which books to carry, school libraries have sometimes been ordered to withdraw certain books from general circulation, usually after some parents' complaints. Librarians often simply comply instead of arguing the case (easier that way). Here's
a list of frequently challenged books, 2000 - 2009.
PS: Am I the only one who this thread's title reminds of something written by
The Onion?