I'm with Rickair. He is credible USERRA IMHO.
All military service members must read USERRA.
You should not provide documentation outside USERRA. DOL VETS will simply say you should understand that an employer can ask for whatever they want. You only must follow USERRA. In this case, under 30 days Don't provide the non USERRA required documentation. Employers will ask, but cannot demand. They will demand often to see what one will provide.
Also, documentation does not have to be orders. Employers may not like the USERRA acceptable documentation, but if you follow USERRA, they have no recourse. Read the following gouge
Home Page
Read the Law Review Index (Left top of page)
Also:
Employer Support of the Guard and Reserve > USERRA > USERRA for Service Members
Thumbnail sketch.
ESGR is liaison, no enforcement, good objective source of info for employers, hopefully helpful. Many employers know they do not have enforcement capability and not likely to get an employer to move their position. Good first move, but a DOL VETS complaint is the start of "real" enforcement.
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Airlines and other employers do have USERRA revisions in their sights in DC.
They also lobby DOD for more restrictive than USERRA guidance. It has happened in the USAFR and USNR in the past. (Provide documentation for less than 30 days etc)