It is illegal for a business to hire unauthorized workers, so employers should check to make sure their workers are authorized to work in the United States. Employers who hire 10 or more unauthorized workers in a year-long period can face imprisonment. All employers are required by law to have all employees sign I-9 forms, certifying the employee is authorized to work. (This is true even if you are certain the employee is authorized). The I-9 must be completed when the employee begins working. Businesses are subject to occasional INS audits.