Firms apply for more employment based green cards and temporary high skilled work visas when the economy is thriving.

FORBES: Positive New Steps To Reform High-Skilled Immigration

For these requirements not to apply, the employment relationship must fall under applicable legal exemptions.

FORBES: 6 Legal Requirements For Unpaid Internship Programs

Its chief tool is E-Verify, an electronic employment eligibility verification system used to weed out unauthorized immigrants when they apply for a job.

FORBES: Arizona-Style Immigration Laws Hurt the Economy

After 10 years, people with provisional legal status could apply for permanent residency if the new security and fencing plans were operating, a new mandatory employment verification system was in place, and a new electronic exit system was tracking who leaves the country.

NPR: GOP: Stronger Borders Or Immigration Bill Will Die