The TN visa category was developed as part of the North American Free Trade Agreement (NAFTA), to facilitate the entry of Canadian and Mexican citizens to the United States to engage in professional business activities on a temporary basis. Only occupations specified in Appendix 1603.D.1 of the NAFTA treaty can serve as the basis for TN employment:
Temporary employees from Canada or Mexico who fit these criteria may be admitted to the US for up to three years at a time.
Canadian citizens do not require a visa from a US consulate, and may apply for TN status at the port of entry to the United States. Citizens of Mexico must apply for a TN visa at a US consulate abroad.