10 U.S.C. § 10212

1. (a)Notwithstanding section 1342 of title 31, the Secretary of Defense may accept the gratuitous services of an officer of a reserve component (other than an officer of the Army National Guard of the United States or the Air National Guard of the United States) in consultation upon matters relating to the armed forces.
2. (b)Notwithstanding section 1342 of title 31, the Secretary of a military department may accept the gratuitous services of an officer of a reserve component under the Secretary’s jurisdiction (other than an officer of the Army National Guard of the United States or the Air National Guard of the United States)—
   1. (1)in the furtherance of the enrollment, organization, and training of that officer’s reserve component or the Reserve Officers’ Training Corps; or
   2. (2)in consultation upon matters relating to the armed forces.