schwit1 sends this quote from the Wall Street Journal:
"Lawmakers working to craft a new comprehensive immigration bill have settled on a way to prevent employers from hiring illegal immigrants: a national biometric identification card all American workers would eventually be required to obtain. Under the potentially controversial plan still taking shape in the Senate, all legal US workers, including citizens and immigrants, would be issued an ID card with embedded information, such as fingerprints, to tie the card to the worker. ... A person familiar with the legislative planning said the biometric data would likely be either fingerprints or a scan of the veins in the top of the hand. It would be required of all workers, including teenagers, but would be phased in, with current workers needing to obtain the card only when they next changed jobs, the person said. The card requirement also would be phased in among employers, beginning with industries that typically rely on illegal-immigrant labor."