5 USC 3321 - Competitive service; probationary period

(a) The President may take such action, including the issuance of rules, regulations, and directives, as shall provide as nearly as conditions of good administration warrant for a period of probation
(1) before an appointment in the competitive service becomes final; and
(2) before initial appointment as a supervisor or manager becomes final.
(b) An individual

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(1) who has been transferred, assigned, or promoted from a position to a supervisory or managerial position, and
(2) who does not satisfactorily complete the probationary period under subsection (a)(2) of this section,

shall be returned to a position of no lower grade and pay than the position from which the individual was transferred, assigned, or promoted. Nothing in this section prohibits an agency from taking an action against an individual serving a probationary period under subsection (a)(2) of this section for cause unrelated to supervisory or managerial performance.

(c) Subsections (a) and (b) of this section shall not apply with respect to appointments in the Senior Executive Service or the Federal Bureau of Investigation and Drug Enforcement Administration Senior Executive Service.