TN related website:

Related immigraiton law

8 CFR 214.6 d) 2):

http://www.nafsa.org/_/file/_/amresource/8cfr2146.htm

http://travel.state.gov/visa/temp/types/types_1274.html

http://www.uscis.gov/portal/site/uscis/menuitem.eb1d4c2a3e5b9ac89243c6a7543f6d1a/?vgnextchannel=bac00b89284a3210VgnVCM100000b92ca60aRCRD&vgnextoid=bac00b89284a3210VgnVCM100000b92ca60aRCRD