The procedure for initially obtaining TN status differs for Mexican and Canadian nationals. The following describes the procedures for both.

A. TN-1, Canadian Professionals.
As nationals of Canada, aliens who qualify for TN-1 status are not required to obtain a visa. Therefore, they may apply directly for TN-1 status at the border. The applicant simply presents his evidence at the border and an interviewing officer reviews the evidence and makes a determination of the applicant's qualifications for TN-1 status based on his review of the submitted material. If approved, the applicant is given an I-94 and proceeds to enter the U.S.

B. TN-2, Mexican Professionals.
The procedure for obtaining TN-2 status is similar to the procedure for obtaining H-1B status. An application, evidence, and documentation must be submitted to the USCIS (formerly called the INS) by mail. If approved, the applicant will receive an approval notice. The applicant then takes this approval notice along with other required materials to the U.S. Consulate where the applicant applies for a visa. As those seeking TN-2 status are Mexican nationals, they are required to obtain a non-immigrant visa to come into the U.S. If a TN-2 visa is issued, then the applicant proceeds to the border and applies for entry into the U.S, as would any other visa holder.

For more information on the TN category, please click one of the following links:
Description
Requirements for a TN status
The detailed list of approved professions for TN status
Application procedure
Benefits of TN status
Limitation of TN status
Renewal TN status
Change of status to TN
Frequently Asked Questions and Answers about TN
PERM-based Green Cards: A Timing Strategy for TN Visa Holder