Both terms describing the United States immigration law seem to be in use, but “Immigration and Nationality Act” seems to be more common (185 Supreme Court references, compared to 8 for Naturalization, and 2249 U.S. Court of Appeals references since 2010, compared to 53 for naturalization). The U.S. Code Annotated Popular Name Table likewise lists “Immigration and Nationality Act,” and the text of federal statutes that refer to the law refers to it only as the “Immigration and Nationality Act.” So while I can’t deny that “Immigration and Naturalization Act” is used on occasion by courts, “Immigration and Nationality Act” seems to be the standard usage.