22 U.S. Code § 3984 - Service in United States and abroad
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.
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.
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.