Orrenius, Pia, and Madeline Zavodny. "Do state work eligibility verification laws reduce unauthorized immigration?". IZA Journal of Development and Migration, Vol.5, No.5 (2016): 1-17.

Orrenius, Pia, and Madeline Zavodny. "Do state work eligibility verification laws reduce unauthorized immigration?". IZA Journal of Development and Migration, Vol.5, No.5 (2016): 1-17.

• In the late 2000s and early 2010s, American states adopted a number of laws designed to reduce illegal immigration, which they claimed the federal government had been failing to do. One common method of this is using the 'E-Verify' system that mandates that employers check all employees in a federal database (1).
• E-Verify is a federal database made available in all states in 2003. It is a voluntary system by which employers can enter their employees' I-9 employment details to be checked against social security and homeland security records. If there is a discrepancy, employees have 8 days to contest, otherwise the employer is required to fire them (3).
• Fraud is only possible in E-Verify through the use of someone else's name and social security number. To address this problem, a photo matching element was added in 2009 to allow visual verification of identity (3).
• Arizona became the first state to mandate the use of E-Verify in the hiring process in 2007. Alabama, Georgia, Mississippi, North Carolina, South Carolina, and Utah have since made the system mandatory for all new hires (3).
• Although all of these states are conservative states in the South or Southwest that received illegal immigrants during the 1990s, this political slant is not likely to be the sole factor in determining their adoption of E-Verify laws since other conservative states in the same region have not done so (11).
• In 2014, there were approximately 11.3 million illegal immigrants in the USA, making up 3% of its population, over 5% of its labor force, and 25% of its immigrant population. These numbers reflect a decline since the 2008 financial crisis, before which upwards of 12.2 million illegal immigrants were resident in the United States, approximately a decline of one million between 2007 and 2009 (1).
• The adoption of E-Verify by states and the tightening of border control have contributed to lower wages paid to illegal immigrants. These wages first fell when the employment of illegal immigrants was criminalized in 1986. Evidence also suggests that states with E-Verify have experienced a decline in the total number of immigrants, as many return to their home countries (2).
• There is evidence to suggest that new illegal immigrants arriving in the USA are less likely to choose states with E-Verify programs and instead move to bordering states. However, evidence suggests that existing illegal immigrants are unlikely to leave a state because it has adopted E-Verify laws and will not move to neighboring states (12). Most illegal aliens who leave a state because of its E-Verify laws tend to return to their country of origin (14).
• The methodology of this study is discussed from page 4 to page 11. 
• "Our results together with previous findings that E-Verify laws and other enforcement measures generally lead to worse labor market outcomes among likely unauthorized immigrants may give policymakers additional reason to consider adopting such policies if they hope to reduce the number of unauthorized immigrants in the USA and are not concerned about adverse effects on those who remain" (14).