22 U.S.C. § 4007: Retirement for expiration of time in class

career members of the Senior Foreign Service, Foreign Service officers, and other career members of the Service who are in such occupational categories as may be designated by the Secretary and who are assigned to salary classes in the Foreign Service Schedule to which Foreign Service officers may also be assigned. Maximum time in class limitations under this subsection (which may not be less than 3 years for career members of the Senior Foreign Service) may apply with respect to the time a member may remain in a single salary class or in a combination of salary classes. the period which the member would have been permitted to remain in class but for the decrease in maximum time in class, or such minimum period as the Secretary determines is necessary to provide members of the Service who are in the same category and salary class as that member a reasonable opportunity to be promoted into the next higher class or combination of classes, as the case may be. after they have attained the highest salary class for their respective occupational categories, or in the case of members of the Senior Foreign Service, while they are in salary classes designated by the Secretary, whose maximum time in class under subsection (a) expires and who is not promoted to a higher class or combination of classes, as the case may be, or whose limited career extension under subsection (b) expires and is not renewed, the career appointment of a member of the Service whose maximum time in class under subsection (a) expires, or whose limited career extension under subsection (b) expires, while that member is occupying a position to which he or she was appointed by the President, by and with the advice and consent of the Senate, shall be extended until the appointment to that position is terminated; and if the Secretary determines it to be in the public interest, the Secretary may extend temporarily the career appointment of a career member of the Service whose maximum time in class or limited career extension expires, but in no case may any extension under this paragraph exceed one year and such extensions may be granted only in special circumstances.