The applicant needs the actual lawful basis permitting the proposed work before beginning it. An unfinished letter or pending preparation does not authorize employment. Review any existing status and the intended activities; do not treat the first day as exempt because later documentation is expected.
Adjust the operational sequence
Ask which tasks can lawfully be performed from the intended location while the required step remains outstanding. Do not use a different entry description to begin the same unauthorized employment. The employer’s willingness to complete the letter afterward cannot retroactively resolve the issue.
TN analysis starts with eligible Canadian or Mexican citizenship, a listed professional occupation, the required qualifications, and a genuine temporary engagement for a US employer. It cannot be used where the applicant is in substance self-employed. A Canadian outside the country may request TN admission through border inspection or preclearance, or the employer may submit an I-129 petition to USCIS when that route fits the facts. Sequence the analysis before the first productive US workday: identify the professional category, assemble the employer record, choose the appropriate entry or petition route, and obtain the required permission. A project manager's urgency cannot replace that order. Compare the proposed start date with the date the support letter, qualifications, and application route will actually be ready. The common error is describing a work trip as a visit and then performing the same duties that needed review. Hypothetical example: A fisheries biologist is invited to join a US hatchery audit next week. She delays the on-site audit, obtains a letter defining the scientific duties and duration, and arranges the appropriate TN step before participating in the inspection.