What is the law regarding I-9 verification? Is the employer required to keep a copy of the documents provided?

Form I-9 is a Department of Homeland Security (DHS) form. All individuals employed in the United States must complete a Form I-9. The employer will provide the Form I-9. The I-9 verifies the individual's employment eligibility to work in the United States. Salary cannot be paid until the I-9 has been satisfied.

Both parties should maintain their own copies.

Thank you for your answer. I guess my question is the requirement of keeping a copy of the driver license, birth certificate, s.s. card etc... If an HR department is audited and they do not have copies of these items to support the information on the I-9 will they be penalized?