5 U.S.C. § 5335: Periodic step-increases

each 52 calendar weeks of service in pay rates 1, 2, and 3; each 104 calendar weeks of service in pay rates 4, 5, and 6; or each 156 calendar weeks of service in pay rates 7, 8, and 9; the employee did not receive an equivalent increase in pay from any cause during that period; and the work of the employee is of an acceptable level of competence as determined by the head of the agency. Under regulations prescribed by the Office of Personnel Management, the benefit of successive step-increases shall be preserved for employees whose continuous service is interrupted in the public interest by service with the armed forces or by service in essential non-Government civilian employment during a period of war or national emergency. When a determination is made under subsection (a) of this section that the work of an employee is not of an acceptable level of competence, the employee is entitled to prompt written notice of that determination and an opportunity for reconsideration of the determination within his agency under uniform procedures prescribed by the Office of Personnel Management. If the determination is affirmed on reconsideration, the employee is entitled to appeal to the Merit Systems Protection Board. If the reconsideration or appeal results in a reversal of the earlier determination, the new determination supersedes the earlier determination and is deemed to have been made as of the date of the earlier determination. The authority of the Office to prescribe procedures and the entitlement of the employee to appeal to the Board do not apply to a determination of acceptable level of competence made by the Librarian of Congress. An increase in pay granted by statute is not an equivalent increase in pay within the meaning of subsection (a) of this section. This section does not apply to the pay of an individual appointed by the President, by and with the advice and consent of the Senate. In computing periods of service under subsection (a) in the case of an employee who moves without a break in service of more than 3 days from a position under a nonappropriated fund instrumentality of the Department of Defense or the Coast Guard described in section 2105(c) to a position under the Department of Defense or the Coast Guard, respectively, that is subject to this subchapter, service under such instrumentality shall, under regulations prescribed by the Office, be deemed service in a position subject to this subchapter. Under procedures established by the Secretary of Defense, upon a determination by the Secretary that the work of an employee is not at an acceptable level of competence, the period of time during which the work of the employee is not at an acceptable level of competence shall not count toward completion of the period of service required for purposes of subsection (a) of section 5335 of title 5 , United States Code, or subsection (e)(1) or (e)(2) of section 5343 of such title. Subsection (a) shall not apply with respect to any period of service performed before the date of the enactment of this Act [ Nov. 25, 2015 ].”