"Undocumented immigrants pay billions of dollars in federal taxes every year by filing annual returns or having money withheld from their paychecks.
An estimated half β possibly more β of the roughly 11 million undocumented immigrants in the country file income tax returns to document their contributions to the United States, researchers say. Because most are ineligible for Social Security numbers, the IRS allows them to file with individual taxpayer numbers, known as ITINs, instead.
Tax data can provide precise information about potentially undocumented immigrants, including their addresses, family structures, and bank and employment information, experts say."