Do you have a source for that?
Yes--34 years of experience--14 first-hand inside the IRS, 20 since leaving. My current and past clients included construction companies and landscapers who had to compete with other companies hiring illegals, and competing against the illegals themselves. The illegals started out working as W-2 employees under bogus SSN's, but in recent years have progressed to the Independent Contractor scam.
With all the preferences accorded to illegals because of the fear of being branded "racist", it is very easy for an illegal to start a business (most don't even bother filing incorporation papers at all--just give the general contractor their "Business" name and a bogus EIN)