TITLE 15 - US CODE - SUBCHAPTER I - NET INCOME TAXES

15 USC 381 - Imposition of net income tax

(a) Minimum standards 
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:
(1) the solicitation of orders by such person, or his representative, in such State for sales of tangible personal property, which orders are sent outside the State for approval or rejection, and, if approved, are filled by shipment or delivery from a point outside the State; and
(2) the solicitation of orders by such person, or his representative, in such State in the name of or for the benefit of a prospective customer of such person, if orders by such customer to such person to enable such customer to fill orders resulting from such solicitation are orders described in paragraph (1).
(b) Domestic corporations; persons domiciled in or residents of a State 
The provisions of subsection (a) of this section shall not apply to the imposition of a net income tax by any State, or political subdivision thereof, with respect to
(1) any corporation which is incorporated under the laws of such State; or
(2) any individual who, under the laws of such State, is domiciled in, or a resident of, such State.
(c) Sales or solicitation of orders for sales by independent contractors 
For purposes of subsection (a) of this section, 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.
(d) Definitions 
For purposes of this section
(1) the term independent contractor means a commission agent, broker, or other independent contractor who is engaged in selling, or soliciting orders for the sale of, tangible personal property for more than one principal and who holds himself out as such in the regular course of his business activities; and
(2) the term representative does not include an independent contractor.

15 USC 382 - Assessment of net income taxes

(a) Limitations 
No State, or political subdivision thereof, shall have power to assess, after September 14, 1959, any net income tax which was imposed by such State or political subdivision, as the case may be, for any taxable year ending on or before such date, on the income derived within such State by any person from interstate commerce, if the imposition of such tax for a taxable year ending after such date is prohibited by section 381 of this title.
(b) Collections 
The provisions of subsection (a) of this section shall not be construed
(1) to invalidate the collection, on or before September 14, 1959, of any net income tax imposed for a taxable year ending on or before such date, or
(2) to prohibit the collection, after September 14, 1959, of any net income tax which was assessed on or before such date for a taxable year ending on or before such date.

15 USC 383 - Net income tax defined

For purposes of this chapter, the term net income tax means any tax imposed on, or measured by, net income.

15 USC 384 - Separability

If any provision of this chapter or the application of such provision to any person or circumstance is held invalid, the remainder of this chapter or the application of such provision to persons or circumstances other than those to which it is held invalid, shall not be affected thereby.