No doubt you are aware that only citizens, lawful permanent residents or nonimmigrants with work authorization may work in the United States. It has come to our attention that employers providing services at federal installations should be especially aware of this requirement. The United States Army and other federal installation landlords routinely examine the identity papers of workers entering their facilities. If the work authorized immigration status for such persons cannot be readily ascertained, these workers are being referred to Immigration and Customs Enforcement for further processing. Thus, you are urged to ensure that: (1) your workers are "employment-authorized;" and (2) your workers are able to establish this readily and convincingly, particularly if employed on a federal installation.