20 CFR §1002.210
What seniority rights does an employee have when reemployed following a period of uniformed service?
The employee is entitled to the seniority and seniority-based rights and benefits that he or she had on the date the uniformed service began, plus any seniority and seniority-based rights and benefits that the employee would have attained if he or she had remained continuously employed. In determining entitlement to seniority and seniority-based rights and benefits, the period of absence from employment due to or necessitated by uniformed service is not considered a break in employment. The rights and benefits protected by USERRA upon reemployment include those provided by the employer and those required by statute. For example, under USERRA, a reemployed service member would be eligible for leave under the Family and Medical Leave Act of 1993, 29 U.S.C. 2601-2654 (FMLA), if the number of months and the number of hours of work for which the service member was employed by the civilian employer, together with the number of months and the number of hours of work for which the service member would have been employed by the civilian employer during the period of uniformed service, meet FMLA's eligibility requirements. In the event that a service member is denied FMLA leave for failing to satisfy the FMLA's hours of work requirement due to absence from employment necessitated by uniformed service, the service member may have a cause of action under USERRA but not under the FMLA.