No. An employer’s new start date does not itself authorize work performed in the United States. Assess the actual location, activity and applicable status before beginning.
Link the start to a confirmed immigration step
Identify whether the applicant is waiting for a visa, admission or another required decision. Have material amendments reviewed before relying on the earlier file. A request to start quickly does not transform professional work into a visitor activity or establish TN status. Coordinate a realistic employer plan while keeping government processing and the employer’s preferred date as separate facts.
Sequence preparation from the employer's genuine start need backward: confirm citizenship, classify the occupation, test its minimum credential, obtain the letter or contract, and only then choose travel or Form I-129. Obtain the final employer letter only after the role, supervisor, pay, location, and expected duration are settled; then check whether the degree, licence, and citizenship documents still match that version. Where the employer needs cover in the interim, that is a staffing question to be solved separately rather than a reason to compress the immigration one, and saying so early usually produces a better conversation than discovering it after a second attempt.