TITLE 22 - US CODE - SUBCHAPTER V - CLASSIFICATION OF POSITIONS AND ASSIGNMENTS

22 USC 3981 - Authority of Secretary

The Secretary shall designate and classify positions in the Department and at Foreign Service posts which are to be occupied by members of the Service (other than by chiefs of mission and ambassadors at large). Positions designated under this section are excepted from the competitive service. Position classifications under this section shall be established, without regard to chapter 51 of title 5, in relation to the salaries established under subchapter IV of this chapter. In classifying positions at Foreign Service posts abroad, the Secretary shall give appropriate weight to job factors relating to service abroad and to the compensation practices applicable to United States citizens employed abroad by United States corporations.

22 USC 3982 - Assignments to Foreign Service positions

(a) Positions assignable; basis for assignment 

(1) The Secretary (with the concurrence of the agency concerned) may assign a member of the Service to any position classified under section 3981 of this title in which that member is eligible to serve (other than as chief of mission or ambassador at large), and may assign a member from one such position to another such position as the needs of the Service may require.
(2) In making assignments under paragraph (1), the Secretary shall assure that a member of the Service is not assigned to a position at a post in a particular geographic area exclusively on the basis of the race, ethnicity, or religion of that member.
(b) Filling of positions by members of Service; employment of members of State Department and other agencies 
Positions designated as Foreign Service positions normally shall be filled by the assignment of members of the Service to those positions. Subject to that limitation
(1) Foreign Service positions may be filled by the assignment for specified tours of duty of employees of the Department and, under interagency agreements, employees of other agencies; and
(2) Senior Foreign Service positions may also be filled by other members of the Service.
(c) Charge d’affaires 
The President may assign a career member of the Service to serve as charge daffaires or otherwise as the head of a mission (or as the head of a United States office abroad which is designated under section 3902 (a)(3)1 of this title by the Secretary of State as diplomatic in nature) for such period as the public interest may require.
(d) Competitive ability with respect to chief of mission positions and for assignments outside areas of specialization 
The Secretary of State, in conjunction with the heads of the other agencies utilizing the Foreign Service personnel system, shall implement policies and procedures to insure that Foreign Service officers and members of the Senior Foreign Service of all agencies are able to compete for chief of mission positions and have opportunities on an equal basis to compete for assignments outside their areas of specialization.
[1] See References in Text note below.

22 USC 3983 - Assignments to non-Service and other positions

(a) Positions assignable 
The Secretary may (with the concurrence of the agency, organization, or other body concerned) assign a member of the Service for duty
(1) in a non-Foreign Service (including Senior Executive Service) position in the Department or another agency, or with an international organization, international commission, or other international body;
(2) with a domestic or international trade, labor, agricultural, scientific, or other conference, congress, or gathering;
(3) for special instruction, training, or orientation at or with a public or private organization; and
(4) in the United States (or in any territory or possession of the United States or in the Commonwealth of Puerto Rico), with a State or local government, a public or private nonprofit">nonprofit organization (including an educational institution), or a Member or office of the Congress.
(b) Salary; travel and other expenses 

(1) The salary of a member of the Service assigned under this section shall be the higher of the salary which that member would receive but for the assignment under this section or the salary of the position to which that member is assigned.
(2) The salary of a member of the Service assigned under this section shall be paid from appropriations made available for the payment of salaries and expenses of the Service. Such appropriations may be reimbursed for all or any part of the costs of salaries and other benefits for members assigned under this section.
(3) A member of the Service assigned under subsection (a)(4) of this section to a Member or office of the Congress shall be deemed to be an employee of the House of Representatives or the Senate, as the case may be, for purposes of payment of travel and other expenses.
(c) Length of assignment 
Except as otherwise provided in subsection (d)(5) of this section, assignments under this section may not exceed four years of continuous service for any member of the Service unless the Secretary approves an extension of such period for that member because of special circumstances.
(d) Assignment to the American Institute in Taiwan 

(1) The Secretary may assign a member of the Service, or otherwise detail an employee of the Department, for duty at the American Institute in Taiwan, if the Secretary determines that to do so is in the national interest of the United States.
(2) The head of any other department or agency of the United States may, with the concurrence of the Secretary, detail an employee of that department or agency to the American Institute in Taiwan, if the Secretary determines that to do so is in the national interest of the United States.
(3) In this subsection, the term employee does not include
(A) a noncareer appointee, limited term appointee, or limited emergency appointee (as such terms are defined in section 3132 (a) of title 5) in the Senior Executive Service; or
(B) an employee in a position that has been excepted from the competitive service by reason of its confidential, policy-determining, policy-making, or policy-advocating character.
(4) An assignment or detail under this subsection may be made with or without reimbursement from the American Institute in Taiwan.
(5) The period of an assignment or detail under this subsection shall not exceed a total of 6 years, except that the Secretary (or any other head of a department or agency of the United States, with the concurrence of the Secretary) may extend the period of an assignment or detail for an additional period of not more than 6 years.

22 USC 3984 - Service in United States and abroad

(a) Obligation to serve abroad; length of stay in United States 
Career members of the Service shall be obligated to serve abroad and shall be expected to serve abroad for substantial portions of their careers. The Secretary shall establish by regulation limitations upon assignments of members of the Service within the United States. A member of the Service may not be assigned to duty within the United States for any period of continuous service exceeding eight years unless the Secretary approves an extension of such period for that member because of special circumstances.
(b) Intermittent duty within United States 
Consistent with the needs of the Service, the Secretary shall seek to assign each career member of the Service who is a citizen of the United States (other than those employed in accordance with section 3951 of this title) to duty within the United States at least once during each period of fifteen years that the member is in the Service.
(c) Sabbaticals 
The Secretary may grant a sabbatical to a career member of the Senior Foreign Service for not to exceed eleven months in order to permit the member to engage in study or uncompensated work experience which will contribute to the development and effectiveness of the member. A sabbatical may be granted under this subsection under conditions specified by the Secretary in light of the provisions of section 3396 (c) of title 5, which apply to sabbaticals granted to members of the Senior Executive Service.

22 USC 3985 - Temporary details

A period of duty of not more than six months in duration by a member of the Service shall be considered a temporary detail and shall not be considered an assignment within the meaning of this subchapter.