While I see your reasoning there’s something about working a guy all day and not paying him. This contractor is not doing this to help the country. He’s the lowest form of whales*&t there is and I have no doubt that he’s done it to Americans too.
A contract with a legal alien or a citizen is enforceable at law and we have state and Federal Departments of Labor to ensure that people here legally or citizens receive what they have coming. If they aren't getting it there's a reason the employee doesn't want the law involved. Their own criminal past, back child support are just a few examples.