Link to the Regulations on this subject.
http://ecfr.gpoaccess.gov/cgi/t/tex...div8&view=text&node=8:1.0.1.2.18.0.1.6&idno=8
8 CFR § 214.6 Citizens of Canada or Mexico seeking temporary entry under NAFTA to engage in business activities at a professional level.
(a)
General. Under section 214(e) of the Act, a citizen of Canada or Mexico who seeks temporary entry as a business person to engage in business activities at a professional level may be admitted to the United States in accordance with the North American Free Trade Agreement (NAFTA).
(b)
Definitions. As used in this section, the terms:
Business activities at a professional level means those undertakings which require that, for successful completion, the individual has a least a baccalaureate degree or appropriate credentials demonstrating status as a professional in a profession set forth in Appendix 1603.D.1 of the NAFTA.
Business person, as defined in the NAFTA, means a citizen of Canada or Mexico who is engaged in the trade of goods, the provision of services, or the conduct of investment activities.
Engage in business activities at a professional level means the performance of prearranged business activities for a United States entity, including an individual. It does not authorize the establishment of a business or practice in the United States in which the professional will be, in substance, self-employed. A professional will be deemed to be self-employed if he or she will be rendering services to a corporation or entity of which the professional is the sole or controlling shareholder or owner.
Temporary entry, as defined in the NAFTA, means entry without the intent to establish permanent residence. The alien must satisfy the inspecting immigration officer that the proposed stay is temporary. A temporary period has a reasonable, finite end that does not equate to permanent residence. In order to establish that the alien's entry will be temporary, the alien must demonstrate to the satisfaction of the inspecting immigration officer that his or her work assignment in the United States will end at a predictable time and that he or she will depart upon completion of the assignment.
There is much more to be found in the controlling regulations, please refer to them....
It is NOT illegal to file for adjustment of status while in the U.S. in TN status.
It may be difficult crossing the border until an I-485 has been filed and AP has been obtained.
It may be difficult to renew TN status either via filing with USCIS or at the border dealing with CBP while a the PERM and subsequent I-140 are pending or your priority date is waiting to become current on the Visa Bulletin. These are practical considerations. DHS does not tend to be comprised of "trusting" individuals, they tend to suspect everyone is trying to "outsmart" them and "get away with something" or commit fraud (that is
not to say that you fall into any of those descriptions--that is the DHS perception based on experience). That's the reality.
The way that the "immigrant intent" issue has been defeated is by proving that the "current" TN job is truly "temporary" and that the actual "immigrant intent" is for a future process that you know will take a long time to become a reality
plus by that time, you might even change your mind about it. There are practical reasons why employers do not want to bother trying to help you when it would require paying hefty legal fees to craft a successful application package.
This is the kind of advice I need.