22 U.S. Code § 3966 - Within-class salary increases
(a) Time period; limitation
Any member of the Service receiving a salary under the Foreign Service Schedule shall be advanced to the next higher salary step in the member’s class at the beginning of the first applicable pay period following the completion by that member of a period of—
unless the performance of the member during that period is found in a review by a selection board established under section 4002 of this title to fall below the standards of performance for his or her salary class.
(b) Additional increase for meritorious service
The Secretary may grant, on the basis of especially meritorious service, to any member of the Service receiving an increase in salary under subsection (a) of this section, an additional salary increase to any higher step in the salary class in which the member is serving.