It is all per a federal statute passed in the mid 1990's I think that required papers. But the papers can be forged and bought for about a hundred bucks in MacArthur Park in LA, or so I have read. All employers with any sense have the forged papers in their files, and thus are immune from federal prosecution.
One of the best places I've seen is right outside and next door to the INS center in Fresno. You can get whatever you need without any effort. As you stand in line for your appointment they brazenly walk along the line asking if anyone needs ID of any kind and the guards at the door don't bat an eyelid.