10 U.S.C. § 14303

(a) Officers in Pay Grades O–1 and O–2.— An officer who is on the reserve active-status list of the Army, Navy, Air Force, or Marine Corps and holds a permanent appointment in the grade of second lieutenant or first lieutenant as a reserve officer of the Army, Air Force, or Marine Corps, or in the grade of ensign or lieutenant (junior grade) as a reserve officer of the Navy, may not be promoted to the next higher grade, or granted Federal recognition in that grade, until the officer has completed the following years of service in grade: (1) Eighteen months, in the case of an officer holding a permanent appointment in the grade of second lieutenant or ensign. (2) Two years, in the case of an officer holding a permanent appointment in the grade of first lieutenant or lieutenant (junior grade). (b) Officers in Pay Grades O–3 and Above .— Subject to subsection (d), an officer who is on the reserve active-status list of the Army, Air Force, or Marine Corps and holds a permanent appointment in a grade above first lieutenant, or who is on the reserve active-status list of the Navy in a grade above lieutenant (junior grade), may not be considered for selection for promotion to the next higher grade, or examined for Federal recognition in the next higher grade, until the officer has completed the following years of service in grade: (1) Three years, in the case of an officer of the Army, Air Force, or Marine Corps holding a permanent appointment in the grade of captain, major, or lieutenant colonel or in the case of a reserve officer of the Navy holding a permanent appointment in the grade of lieutenant, lieutenant commander, or commander. (2) One year, in the case of an officer of the Army, Air Force, or Marine Corps holding a permanent appointment in the grade of colonel or brigadier general or in the case of a reserve officer of the Navy holding a permanent appointment in the grade of captain or rear admiral (lower half). This subsection does not apply to an adjutant general or assistant adjutant general of a State or to an appointment in a higher grade which is based upon a specific provision of law. (c) Authority To Lengthen Minimum Period in Grade .— The Secretary concerned may prescribe a period of service in grade for eligibility for promotion, in the case of officers to whom subsection (a) applies, or for eligibility for consideration for promotion, in the case of officers to whom subsection (b) applies, that is longer than the applicable period specified in that subsection. (d) Waivers To Ensure Two Below-the-Zone Considerations .— Subject to section 14307(b) of this title , the Secretary of the military department concerned may waive subsection (b) to the extent necessary to ensure that officers described in paragraph (1) of that subsection have at least two opportunities for consideration for promotion to the next higher grade as officers below the promotion zone.