"You have people who feel that if a school library buys a copy of the Bible, it's a violation of church and state," says James LaRue, who directs the Office for Intellectual Freedom for the American Library Association, which released its annual 10 top snapshot of "challenged" books on Monday, part of the association's "State of Libraries Report" for 2016.

"And sometimes there's a retaliatory action, where a religious group has objected to a book and a parent might respond by objecting to the Bible." LaRue emphasized that the library association does not oppose having Bibles in public schools. Guidelines for the Office for Intellectual Freedom note that the Bible "does not violate the separation of church and state as long as the library does not endorse or promote the views included in the Bible."

The ALA also favors including a wide range of religious materials, from the Quran to the Bhagavad Gita to the Book of Mormon. LaRue added that the association does hear of complaints about the Quran, but fewer than for the Bible.