22 U.S. Code § 3952 - Diplomatic and consular missions
The Secretary of State may recommend to the President that a member of the Service who is a citizen of the United States be commissioned as a diplomatic or consular officer or both. The President may, by and with the advice and consent of the Senate, commission such member of the Service as a diplomatic or consular officer or both. The Secretary of State may commission as a vice consul a member of the Service who is a citizen of the United States. All official functions performed by a diplomatic or consular officer, including a vice consul, shall be performed under such a commission.
Members of the Service commissioned under this section may, in accordance with their commissions, perform any function which any category of diplomatic officer (other than a chief of mission) or consular officer is authorized by law to perform.
The Secretary of State shall define the limits of consular districts.