49 U.S. Code § 14503 - Withholding State and local income tax by certain carriers
(a) Single State Tax Withholding.—
(1) In general.— No part of the compensation paid by a motor carrier providing transportation subject to jurisdiction under subchapter I of chapter 135 or by a motor private carrier to an employee who performs regularly assigned duties in 2 or more States as such an employee with respect to a motor vehicle shall be subject to the income tax laws of any State or subdivision of that State, other than the State or subdivision thereof of the employee’s residence.
(2) Employee defined.— In this subsection, the term “employee” has the meaning given such term in section 31132.
(b) Special Rules.—
(1) Calculation of earnings.— In this subsection, an employee is deemed to have earned more than 50 percent of pay in a State or subdivision of that State in which the time worked by the employee in the State or subdivision is more than 50 percent of the total time worked by the employee while employed during the calendar year.
(2) Water carriers.— A water carrier providing transportation subject to jurisdiction under subchapter II of chapter 135 shall file income tax information returns and other reports only with—
(A) the State and subdivision of residence of the employee (as shown on the employment records of the carrier); and