Definitions of "profession" often require that a code of ethics be among the salient characteristics. The American Library Association first promulgated such a code in 1938; the current code, last amended in 2008, can be found at http://www.ala.org/ala/issuesadvocacy/proethics/index.cfm (see the following page).
Other library associations have codes of ethics also, usually published in their membership handbooks. A few of these are included in an appendix in Information Ethics: Concerns for Librarianship and the Information Industry (McFarland, 1990). Of special interest is the California Library Association's "Statement of Professional Responsibility for Librarians," primarily because it is so detailed and comprehensive.
Note that the California document does not use the term "ethics." Neither does that of the American Society for Information Science & Technology (ASIS&T), which is called "ASIS Professional Guidelines." In fact, an earlier draft version states that it "is not intended to be a regulatory code, with sanctions for those who violate its provisions." Since ASIS members belong to various professions that have codes of their own (e.g., engineers, librarians), the ASIS&T statement merely purports "to articulate the distinctive goals and ideals of the information profession, to guide the activities of its members, and to direct their thoughts into reflection on the ethical aspects of the profession." (Information Ethics, p. 63).
The Special Libraries Association (SLA) also prefers to relate its "statement on professional conduct" to the organizational context, as is evident in the document reproduced in the next section. You are urged to compare the ALA, SLA, and other association statements, as they shed light on the commonalities and divergences of the various branches of the library/information professions. Be sure to check the archivists' code and that of the Association of Independent Information Professionals, as they are not only substantially different but provide insight into the nature of those branches of the information professions.
SLA has a quite comprehensive list of ethics statements on its members only website. You might also find it interesting to see the codes of associations in other parts of the world. Go to the IFLA site at http://www.ifla.org/en/node/623