If you're facing an employment lawsuit, don't bother probing into the employee's immigration status during the lawsuit's discovery phase. The EEOC has long held that immigration status is irrelevant to any underlying discrimination claims, and a recent federal court ruling supports that stance.
The case involved a female restaurant employee in Minnesota who claimed sexual harassment. The EEOC sued on her behalf. During discovery, the restaurant's attorneys asked about the woman's immigration status. EEOC attorneys objected and the judge agreed, barring any questions designed to elicit whether the woman is in the country legally. (EEOC v. The Restaurant Company)
According to EEOC attorney Tina Burnside, "Certain defense lawyers ... figure that they can put such fear into the hearts of the victims that they will walk away. The line of inquiry has nothing to do with the merits in employment discrimination cases. It's good that the courts are seeing through it and are not permitting it."