20 CFR §1002.248
What constitutes cause for discharge under USERRA?
The employee may be discharged for cause based either on conduct or, in some circumstances, because of the application of other legitimate nondiscriminatory reasons.
(a) In a discharge action based on conduct, the employer bears the burden of proving that it is reasonable to discharge the employee for the conduct in question, and that he or she had notice, which was express or can be fairly implied, that the conduct would constitute cause for discharge.
(b) If, based on the application of other legitimate nondiscriminatory reasons, the employee's job position is eliminated, or the employee is placed on layoff status, either of these situations would constitute cause for purposes of USERRA. The employer bears the burden of proving that the employee's job would have been eliminated or that he or she would have been laid off.