5 C.F.R. § 352.208

(a) Employee's right to reemployment. An employee is entitled to be reemployed by the reemploying agency as promptly as possible but not more than 30 calendar days after receipt of his application. Except as provided in paragraph (c) of this section, the employee is entitled to reemployment in the occupational field and at the same grade or level and in the same geographical area as the position which the employee last held in that agency. If the reemployment would cause the separation or demotion of another employee, the applicant shall then be considered an employee for the purpose of applying the reduction-in-force regulations (5 CFR part 351) to determine to what, if any, position, he or she is entitled.

(b) Reemployment in a higher grade. The reemploying agency may reemploy the employee in a position of higher grade than that to which he is entitled, but not if this reemployment would cause the displacement of another employee.

(c) Reemployment in SES. When the employee's right is to a position in the SES, reemployment or return may be to any position in the SES for which the employee is qualified.

(d) Seniority in postal service. On reemployment in the postal service, the employee is entitled to the seniority he would have attained had he remained in the postal service.

(e) Basis for agency refusal to reemploy. An agency may refuse to reemploy under this section only when the employee was last separated for serious cause evidencing his unsuitability for reemployment.