In order to maintain your status in the U.S., TN-1 non-immigrant visa holders should ensure that their passport remains valid at all times, ideally up to 6 months into the future. ISSS strongly recommends that you have a passport valid at least 6 months into the future at the time of filing for an extension of stay or amendment of stay.
Always ensure that your passport is valid at least 6 months into the future when you travel outside of the U.S. Entering the U.S. with a passport that expires within 6 months from the date of entry will subject you to a shortened period of authorized stay. Upon inspection, CBP will stamp your validity to remain in the U.S. based upon the expiration date of your passport, not your I-797 approval notice if your passport expires within 6 months. This will create the need to file an extension of your stay prematurely.