The Copyright Law of the United States (Title 17, United States Code) governs the making of photocopies or other reproduction restrictions of copyrighted material.
Under certain conditions specified in the law, libraries and archives are authorized to furnish photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be used for any reproduction purposes in excess of "fair use." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use", that user may be liable for copyright infringement.
This institution reserves the right to refuse to accept a copying order "if in its judgment, fulfillment of the order would involve violation of copyright law."
Official text of the copyright warning sign from the Federal Register (November 16, 1977)