BY MIRIAM JORDAN

MINNEAPOLIS—In 2009, Alba and Eugenio were making almost twice the federal minimum wage, plus benefits, cleaning a skyscraper for a national janitorial company. With two toddlers, the Mexican couple enjoyed relative prosperity in a tidy one-bedroom duplex in a working-class neighborhood here.

Late that year, federal agents audited employee records of ABM Industries Inc., forcing it to shed all the illegal workers on its payrolls in the Twin Cities. Among them was the couple, undocumented immigrants who had worked at ABM for more than a decade.

Shortly after, Alba and Eugenio, who declined to have their surname published, landed at ...

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