As a life long bookkeeper, I can assure you that the laws regarding hiring non-citizens, etc, have been in place for over 40 years. The biggest problem is that employers—small contractors for example, cash checks from clients & pay CASH to those workers. I once did the books for a roofing company. Took me MONTHS to figure out that was happening. 18 employees on the books-—18 more getting CASH ....for years before I got there. I refused to sign any more payroll reports after that.
And those business owners making cash payments, no doubt, also counted those payments to the laborers as a business expense.
That reduced their taxable income and lowered the amount of taxes they paid.
If these businesses don’t take the deductions and still make cash payments, then, mathematically, the business owner would increase his after-tax income by hiring a legal worker for whom he could make deductions.
Break Even Legal Worker Wage = (illegals’ wage)/(1 - marginal tax rate)