If you believe your USERRA rights may have been violated, you may file a formal complaint with the U.S. Department of Labor, Veterans Employment & Training Service (DOL-VETS):
The DOL-VETS USERRA complaint form, VETS-1010, and instructions for completing and submitting it, are available here;
The contact information for your local DOL-VETS office is available here;
If you choose to file a USERRA complaint, DOL-VETS will investigate and attempt to resolve it; if efforts at resolution are unsuccessful, you may have the option of seeking representation from either OSC (if the complaint involves a federal executive agency, with certain limited exceptions) or the U.S. Department of Justice (if the complaint involves a state, local, or private employer).
At various stages before and during the complaint process, you may also have the option of filing an action with the Merit Systems Protection Board (MSPB) (if the complaint involves a federal executive agency, with certain limited exceptions) or in federal or state court (if the complaint involves a state, local, or private employer).