During a recent liaison meeting with the American Immigration Lawyers Association, the U.S. Department of State (DOS) confirmed that a Mexican citizen's TN visa stamp remains valid despite a change in employer.
For example, if a Mexican citizen working in the U.S. under TN status for company ABC later files an I-129 petition to work for company XYZ, the individual may continue to use his/her TN visa stamp from company ABC for travel until the visa stamp expires. The DOS recommended that such individuals travel with their I-797 approval notice for the new company in case it is requested by U.S. border officials. AILA/DOS Liaison, AILA Doc. No. 16100705 (posted 10/7/16).