First, the simple answer: employers should use the most recent Form I-9 found at www.uscis.gov/i-9. The form indicates the most recent revision date on the lower right hand corner: Rev. 08/07/09. Also acceptable is the immediately prior version of the form dated 02/02/09 on the lower right hand corner.
Now for the recent history of the I-9. On December 17, 2008, United States Citizenship and Immigration Services (USCIS) published an interim final rule that amended Form I-9 and revised the list of documents acceptable for employment verification. Use of the new revision, dated 02/02/09 on the lower right hand corner, became mandatory for all employers beginning April 3, 2009. However, employer confusion was created by the fact that the form also carried an Office of Management and Budget (OMB) expiration of June 30, 2009. USCIS advised employers that the form could continue to be used despite the OMB expiration. USCIS released an updated Form I-9 in August 2009 (dated 08/07/09 on the lower right hand corner) with an updated OMB expiration of 08/31/12. For simplicity, it is recommended that employers use the most recent form with the 08/07/09 date even though USCIS has indicated employers may continue to use the 02/02/09 form as well.
Key tips for employers: use only the new Form I-9 for newly-hired employees; use only the new Form I-9 for any necessary reverifications or I-9 updating performed as part of complying with the new E-Verify requirement placed on certain federal contractors; and remember that the documents acceptable for I-9 completion have changed, the most notable of which is the fact that expired documents can no longer be accepted. Please consult the instructions to the new Form I-9 and provide employees with the new document list at the time of document completion.