20 C.F.R. § 1002.7
How does USERRA relate to other laws, public and private contracts, and employer practices?
(a) USERRA establishes a floor, not a ceiling, for the employment and reemployment rights and benefits of those it protects. In other words, an employer may provide greater rights and benefits than USERRA requires, but no employer can refuse to provide any right or benefit guaranteed by USERRA.
(b) USERRA supersedes any State law (including any local law or ordinance), contract, agreement, policy, plan, practice, or other matter that reduces, limits, or eliminates in any manner any right or benefit provided by USERRA, including the establishment of additional prerequisites to the exercise of any USERRA right or the receipt of any USERRA benefit. For example, an employment contract that determines seniority based only on actual days of work in the place of employment would be superseded by USERRA, which requires that seniority credit be given for periods of absence from work due to service in the uniformed services.
(c) USERRA does not supersede, nullify or diminish any Federal or State law (including any local law or ordinance), contract, agreement, policy, plan, practice, or other matter that establishes an employment right or benefit that is more beneficial than, or is in addition to, a right or benefit provided under the Act. For example, although USERRA does not require an employer to pay an employee for time away from work performing service, an employer policy, plan, or practice that provides such a benefit is permissible under USERRA.
(d) If an employer provides a benefit that exceeds USERRA's requirements in one area, it cannot reduce or limit other rights or benefits provided by USERRA. For example, even though USERRA does not require it, an employer may provide a fixed number of days of paid military leave per year to employees who are members of the National Guard or Reserve. The fact that it provides such a benefit, however, does not permit an employer to refuse to provide an unpaid leave of absence to an employee to perform service in the uniformed services in excess of the number of days of paid military leave.