The Gun Control Act (GCA) makes it unlawful for certain categories of persons to ship, transport, receive, or possess firearms. 18 USC 922(g). Transfers of firearms to any such prohibited persons are also unlawful. 18 USC 922(d).
These categories include any person:
Under indictment or information in any court for a crime punishable by imprisonment for a term exceeding one year;
convicted of a crime punishable by imprisonment for a term exceeding one year;
who is a fugitive from justice;
who is an unlawful user of or addicted to any controlled substance;
who has been adjudicated as a mental defective or has been committed to any mental institution;
who is an illegal alien;
who has been discharged from the military under dishonorable conditions;
who has renounced his or her United States citizenship;
who is subject to a court order restraining the person from harassing, stalking, or threatening an intimate partner or child of the intimate partner; or
who has been convicted of a misdemeanor crime of domestic violence (enacted by the Omnibus Consolidated Appropriations Act of 1997, Pub. L. No. 104-208, effective September 30, 1996). 18 USC 922(g) and (n).