How Can an Applicant Apply for TN Status if Already in the U.S.?
If the Canadian or Mexican citizen is already in the United States in another nonimmigrant classification (e.g., F-1, H-1B, etc.), he may elect to file an application (Form I-129) with USCIS to change his status to TN, without traveling outside the United States. Under these circumstances, the applicant must be maintaining a valid nonimmigrant status to be eligible for a change of status, and must wait until the change of status is approved before he begins employment in TN status.
If a Mexican citizen changes to TN status while in the U.S., the next time he leaves the U.S., he must obtain a TN or TD visa before returning to the U.S. to resume work in TN status.