U.S. Consulates have issued some Mexican nationals NAFTA TN Visas with a validity period for up to 2 -3 years pursuant to a 2004 Department of State Memorandum. This has lead to some confusion with U.S. Customs and Border Protection in the issuance of I-94s. In these situations, CBP has issued some TN I-94s for more than one year, contrary to U.S. immigration regulations that limit the authorized period of stay for TN workers to one year.
CBP has clarified that at a land border, a Mexican national TN applicant who holds a TN visa should be issued a multiple entry I-94 valid for one year. If the applicant holds a TN visa that is valid for 2 or 3 years, CBP has explained that this individual may “renew” his or her TN status by presenting a new TN support letter from the employer. CBP has stated that complete re-adjudication of the TN is not necessary in this scenario. Nevertheless, it has noted that it retains the right to request additional documentation as needed. Thus, when seeking a “renewal” it may be prudent to return to the border with a complete set of TN application materials.
-From AILA/CBP Liaison Committee Discussion (March 22, 2006).