10 U.S.C. § 143

(a) Permanent Limitation on OSD Personnel .— The number of OSD personnel may not exceed 4,300. (b) OSD Personnel Defined .— For purposes of this section, the term “OSD personnel” means military and civilian personnel of the Department of Defense who are assigned to, or employed in, functions in the Office of the Secretary of Defense (including Direct Support Activities of that Office and the Washington Headquarters Services of the Department of Defense). (c) Limitation on Reassignment of Functions .— In carrying out reductions in the number of personnel assigned to, or employed in, the Office of the Secretary of Defense in order to comply with this section, the Secretary of Defense may not reassign functions solely in order to evade the requirements contained in this section.