He is. He really is.
it's easy to show you are a citizen. Birth certificate, passport, realID (enhanced driver's license), naturalization certificate, etc.
He should pay attention to IS9...that form you fill out when you get hired somewhere that shows you are a citizen.
Is any worker getting paid 'under the table'? That's cause right there to go after such a company for violating hiring laws and ignoring immigration law.
Oh...and then there is always the freeloaders taking over hotels as illegal immigrants. They're pretty easy to find. Then there is the Venezuelan gangs...go round them up too.