Hell, they'll just drop the back-tax requirement. Remember, cheap labor at any cost.
So after they become citizens, they'll continue to receive money under the table (thereby saving their employers a bundle in labor costs)? Somehow, I don't think so.
Since current immigration laws aren't being enforced at all, in order to get amnesty for our "guest workers" what will happen is they will be required to fulfill several onerous conditions, much more complicated than simply arresting and deporting them, which they will simply ignore.
This can be seen on the face of the Senate bill, but our Fearless Leaders continue with this charade, apparently thinking that we are sheep, while they are the sheepdogs.