5 C.F.R. § 353.209 – Retention protections.

(a) During uniformed service. An employee may not be demoted or separated (other than military separation) while performing duty with the uniformed services except for cause. (Reduction in force is not considered “for cause” under this subpart.) He or she is not a “competing employee” under § 351.404 of this chapter. If the employee's position is abolished during such absence, the agency must reassign the employee to another position of like status, and pay.
(b) Upon reemployment. Except in the case of an employee under time-limited appointment who finishes out the unexpired portion of his or her appointment upon reemployment, an employee reemployed under this subpart may not be discharged, except for cause—
1. (1) If the period of uniformed service was more than 180 days, within 1 year; and
2. (2) If the period of uniformed service was more than 30 days, but less than 181 days, within 6 months.