It is unlawful for an employer to hire or employ a person who is not a citizen or otherwise authorized to work in the United States.
If the I-9 form is not properly signed or dated, or missing information, there can be huge paperwork penalties that amount to tens of thousands of dollars. This Houston immigration lawyer and Miami immigration lawyer has defended businesses on such cases in the past, helping clients to avoid huge penalties.
The other issue is that if ICE wants to, they can criminally charge the employer and arrest the owners of the business if they find any undocumented workers. It is very important for employers to make sure that their workers are all properly documented, or the employer should consider terminating the worker or helping them to apply for a work permit. Even for undocumented workers, there are often ways to get work permits.