I-9 Immigration Forms. Employers must retain an employee's completed form I-9 for as long as the individual works for the employer. Once the individual's employment has terminated, the employer must determine how long after termination the Form I-9 must be retained, which is either three years after the date of hire, or one year after the date employment is terminated, whichever is later. Forms I-9 can be retained either on paper or microform, or electronically.