Peggy told her manager, Barry, and the HR department that she is leaving for military service. Barry told her not to worry — that her job will be waiting for her but, because of budget constraints, he may not be able to offer her a promotion upon her return. Can Barry require Peggy to waive her promotion before she goes on military leave?
No. In this instance, Peggy cannot be asked to waive her promotion because her right to a promotion hasn’t matured yet. Under the Uniformed Services Employment and Reemployment Rights Act (USERRA), waivers of rights, whether explicitly or impliedly through conduct, are permissible as long as they are clear, convincing, specific, unequivocal, and not under duress. Generally, however, only known rights that already have matured can be waived. Before entering military service, an employee cannot waive rights or benefits that are contingent upon reemployment. Therefore, Peggy cannot be asked to waive her right to a promotion in advance.
Source: When Duty Calls; Military Leave and Veterans’ Rights.