This is a subject of great familiarity to the Treehouse. It is not necessarily an Eric Holder / President Obama construct either.
According to EEO law it is unlawful to check the work authorization of any employment applicant, IF the screening has a disparate impact on a federally protected category of personage.  In reality the law, as applied, means you cannot check the employment eligibility of applicants if the screening creates disqualified applicants who are  disproportionately Latino (race discrimination); which they automatically will be.
Ergo -technically, and lawfully- you cannot screen applicants for residency or employment eligibility.   That is why fake documents are so easy for an illegal to use to gain employment; the employer is not allowed to check, or verify, their legitimacy.

(Via Daily Caller) A Texas catering business will pay the United States $26,400 for engaging in “citizenship-discrimination,” as part of a settlement with the Justice Department announced Tuesday.
Culinaire International unlawfully discriminated against employees based on their citizenship status, the Justice Department claimed, because it required non-citizen employees to provide extra proof of their right to work in the United States.
Culinaire has agreed to pay the United States $20,460 in civil penalties, receive training in anti-discrimination rules of the Immigration and Nationality Act, revise its work eligibility verification process, and create a $40,000 back pay fund for “potential economic victims.”
“Employers cannot discriminate against workers by requiring them to produce more documents than necessary in the employment eligibility verification and reverification processes,” Acting Assistant Attorney General for the Civil Rights division, Molly Moran, said in a statement.
A lawful permanent resident’s card expires, but their right to work is permanent, and in this case Culinaire was requiring employees to present a renewed permanent resident card to be verified as work-eligible. The Justice Department claimed this violated a provision in the INA that prohibits employers from requiring extra documentation from non-citizen employees. (read more)

It’s the biggest open secret that NOBODY understands !