When a non-immigrant worker files an I-129 petition to obtain employment authorization for a new employer, the I-797 approval notice issued does not normally provide the individual with travel authorization. In order to travel under the newly approved status, the individual generally needs to possess a valid visa stamp from the U.S. consulate.
Within the TN visa classification context, there is an exception to this rule: Citizens of Canada are exempt from the visa stamp requirement, and so may travel just with the I-797 approval notice. Mexican citizens, on the other hand, are not exempt, and must have a valid TN visa stamp from the U.S. consulate in order to travel.
The U.S. government has never clearly stated whether a Mexican citizen who already has a valid TN visa stamp may re-enter the U.S. with this TN visa stamp after filing a Form I-129 and obtaining TN visa status employment authorization for a new employer.
I had previously written that under legacy INS guidance discussing the H-1B visa and other visa classifications, such travel should be allowed even though this guidance did not specifically deal with the TN visa classification.
In a liaison meeting with AILA, the Chicago CBP office has confirmed that in this situation, an individual may re-enter the U.S. under the previously issued TN visa provided he/she has documentation evidencing the new employment arrangement. AILA Chicago Ch. / CBP - Chicago Meeting, Oct. 14, 2011, AILA InfoNet Doc. No. 11120166 (Posted 12/01/11).