These unions would build that wall quickly if that was even thought of doing.
The Unions could give a damn. All they really care about is dues. I did a job at a rather large national union and they had to developer a special algorithm to handle multiple members using the same social security number in order to keep track properly of their contributions to the retirement fund. I was ludicrous we had as many as 20+ people using the same ss#. BTW I quit that job before anyone decides to give me a bunch of crap.