TN Visa required if working for a Canadian Company?

I work for a Canadian engineering consulting firm. I am an engineering technologist, with a degree in one engineering discipline and a certificate in another. The Canadian firm pays my wages and benefits, supplies my supervision, and hands my income tax to CRA. I spend the bulk of my time in Canada, and the bulk of the actual work I do takes place in Canada, wherever the customer is located.

We have customers and projects in the US. At times, we need to go to site to review the facilities and collect information. Then we go home, work up the design, submit it to the client, who then gets the ball rolling to have it built by US contractors. During construction, we go to site to make sure it is being built as we designed, and to commission the new equipment when it is built. Do we need TN status to go to the site in the US to do this work?

The NAFTA agreement is not too clear. The various official websites are just as vague. Actual treatment at the border is variable: some agents say we need it, others do not.

From the US Embassy site:

A citizen of a NAFTA country may work in a professional occupation in the U.S. provided that all of these conditions are met:

1. The profession is recognized under NAFTA.
2. The alien possesses the specific criteria for that profession.
3. The prospective position requires someone in that professional capacity.
4. The alien is going to work for a U.S. employer.

My belief is that since we are not being paid directly by the US client,we are not working for them.

Any other experience out there?

Thanks.

To enter US to work, regardless of the employer, a status is needed. The vast majority of such 'business visitors" enter on B1 status. It's undocumented, so many don't realize that they are in a particular status. There is no "undocumented TN" status.

However not all work is pwermitted under B1, and there are instances when a Cdn firm nust request that their US customer, or in most cases subsidiary or siste firm, petitio nthe worker to be allowed entry on TN.

As I said, this is typically when one will be engaged in work which is not permited under B1 entry.

Fortunately almost all engineering work, in support of an existing/continuing project, is eligible for B1.

One would typically carry a copy of the existing WO/PO, and a letter from the US client stating what work is being done, and theat the employee will at all times be paid by the Cdn employer.