The battle over illegal immigration will be won or lost with employers
As MW said, that's only one part of the problem. But unless we become totalitarian, the idea that employer WILL be the solution is a fantasy.

There are mainstream employers that can easily be regulated, But many businesses, like agriculture, landscaping, pot farms, and such, where cash limits documentation of transactions, employers will try to get around the high cost of complying with taxes, withholding, insurance, and other business costs. This is not to mention pure criminal businesses which persist.