Imposition of net income tax

No State, or political subdivision thereof, shall have power to impose, for any taxable year ending after September 14, 1959, a net income tax on the income derived within such State by any person from interstate commerce if the only business activities within such State by or on behalf of such person during such taxable year are either, or both, of the following: The provisions of subsection (a) shall not apply to the imposition of a net income tax by any State, or political subdivision thereof, with respect to— For purposes of subsection (a), a person shall not be considered to have engaged in business activities within a State during any taxable year merely by reason of sales in such State, or the solicitation of orders for sales in such State, of tangible personal property on behalf of such person by one or more independent contractors, or by reason of the maintenance, of an office in such State by one or more independent contractors whose activities on behalf of such person in such State consist solely of making sales, or soliciting orders for sales, or tangible personal property. For purposes of this section—