Yes, all employers in the United States must complete Form I-9 for every individual they hire for employment, regardless of the duration of their employment. This requirement applies to both citizens and noncitizens, and to part-time, temporary, and full-time employees.
Even if an employee is hired to work for only one day, you must still complete and maintain a Form I-9 for that employee. The employee must complete Section 1 of the form on or before their first day of employment, and the employer must complete Section 2 of the form by the end of the employee's third day of employment. Employers are also responsible for retaining the completed Form I-9 for a certain period after the employment relationship ends, as specified by the regulations.