Are Guard or Reserve members who go on active military duty guaranteed a job on their return?
In general, they are entitled to be restored to the position they would have attained had they not entered uniformed service.

Employees who served less than 91 days must be placed in the position for which they are qualified that they would have attained had their employment not been interrupted. If not qualified for such a position after reasonable efforts by the agency to qualify the person, the employee is entitled to be placed in the position he or she left.

Employees who served more than 90 days have essentially the same rights except that the agency has the option of placing the employee in a position for which qualified of like seniority, status, and pay.