Immigration law is an ever-changing subject, which you'll need to keep a sharp eye on if you're affected by it in any way. Congress often tinkers with existing immigration law (though things rarely seem to go anywhere fast), so be sure to keep yourself educated.

According to current immigration law, employers have to regularly check the paperwork for a foreign worker, and must keep it on file for three years after hire or a year after termination, whichever period is longer. Employers can't, however, be held responsible for well-forged paperwork.

If you have any serious questions about immigration law, consult an attorney who specializes in the field. For professional reasons they have to keep themselves up-to-date on all the twists and turns on immigration law, and are far more likely to be able to help you than anyone else.