20 CFR §1002.23
What must the individual show to carry the burden of proving that the employer discriminated or retaliated against him or her?
(a) In order to prove that the employer discriminated or retaliated against the individual, he or she must first show that the employer's action was motivated by one or more of the following:
(1) Membership or application for membership in a uniformed service;
(2) Performance of service, application for service, or obligation for service in a uniformed service;
(3) Action taken to enforce a protection afforded any person under USERRA;
(4) Testimony or statement made in or in connection with a USERRA proceeding;
(5) Assistance or participation in a USERRA investigation; or,
(6) Exercise of a right provided for by USERRA.
(b) If the individual proves that the employer's action was based on one of the prohibited motives listed in paragraph (a) of this section, the employer has the burden to prove the affirmative defense that the action would have been taken anyway absent the USERRA-protected status or activity.