[Old_Mil]

90% are not working in registered businesses. How are you going to find the 90% who are so outside the system that they can't be ID'd? 12-30 million.

...seizure of the property of a landlord who rents to them.
...the cutting off of federal funds to a school that educates them.
...the loss of medicare and medicaid funds to a hospital that treats them.

Even if you could work off the books, would you stay in a country where you would be homeless, have no access to health care, and no access to education?

[EternalVigilance]

Rolling up the welcome mat costs little.

[RightWhale]

would you stay in a country where you would be homeless, have no access to health care, and no access to education?

That is a lot like it is where they come from.