They are not "required to report" anything. They are required to produce records when served with a warrant.
"Section 215: Access to Records Under Foreign Intelligence Security Act (FISA):
Allows an FBI agent to obtain a search warrant for "any tangible thing," which can include books, records, papers, floppy disks, data tapes, and computers with hard drives.
Permits the FBI to compel production of library circulation records, Internet use records, and registration information stored in any medium.
Does not require the agent to demonstrate "probable cause," the existence of specific facts to support the belief that a crime has been committed or that the items sought are evidence of a crime. Instead, the agent only needs to claim that he believes that the records he wants may be related to an ongoing investigation related to terrorism or intelligence activities, a very low legal standard.
Libraries or librarians served with a search warrant issued under FISA rules may not disclose, under of penalty of law, the existence of the warrant or the fact that records were produced as a result of the warrant. A patron cannot be told that his or her records were given to the FBI or that he or she is the subject of an FBI investigation."
http://www.ala.org/alaorg/oif/usapatriotlibrary.html