The initial period of admission into the United States may be up to three (3) years. USCIS, or the CBP agent at a Class “A” Port of Entry, may grant additional three (3) year periods (or extensions) of stay. If the TN nonimmigrant worker is in the United States, his employer may file a petition with USCIS to extend his stay. There is no limit to the number of years a TN nonimmigrant worker can maintain that status in the United States.