Volume 12 – Citizenship & Naturalization, Part A – Citizenship and Naturalization Policies and Procedures
Chapter 3 – USCIS Authority to Naturalize
It has long been established that Congress has the exclusive authority under its constitutional power to establish a uniform rule of naturalization and to enact legislation under which citizenship may be conferred upon persons.  See Chirac v. Chirac, 15 U.S. 259 (1817). Before 1991, naturalization within the United States was a judicial function exercised since 1790 by various courts designated in statutes enacted by Congress under its constitutional power to establish a uniform rule of naturalization.
As of October 1, 1991, Congress transferred the naturalization authority to the Attorney General (now the Secretary of DHS).  See INA 310(a). USCIS is authorized to perform such acts as are necessary to properly implement the Secretary’s authority.  See INA 310. In certain cases, an applicant for naturalization may choose to have the Oath of Allegiance  See INA 337(a). administered by USCIS or by an eligible court with jurisdiction. Eligible courts may choose to have exclusive authority to administer the Oath of Allegiance.
See Chirac v. Chirac, 15 U.S. 259 (1817).