22 U.S. Code § 3949 - Limited appointments
(a) A limited appointment in the Service, including an appointment of an individual who is an employee of an agency, may not exceed 5 years in duration and, except as provided in subsection (b) of this section, may not be extended or renewed. A limited appointment in the Service which is limited by its terms to a period of one year or less is a temporary appointment.
(b) A limited appointment may be extended for continued service—
(3) as a career candidate, if continued service is determined appropriate to remedy a matter that would be cognizable as a grievance under subchapter XI of this chapter;
(4) as a career employee in another Federal personnel system serving in a Foreign Service position on detail from another agency; and
Source(Pub. L. 96–465, title I, § 309,Oct. 17, 1980, 94 Stat. 2086; Pub. L. 100–204, title I, § 176,Dec. 22, 1987, 101 Stat. 1361; Pub. L. 103–236, title I, § 180(a)(1),Apr. 30, 1994, 108 Stat. 415; Pub. L. 103–415, § 1(hh),Oct. 25, 1994, 108 Stat. 4303.)