49 U.S.C. § 14505
State tax
A State or political subdivision thereof may not collect or levy a tax, fee, head charge, or other charge on—
(1)
a passenger traveling in interstate commerce by motor carrier;
(2)
the transportation of a passenger traveling in interstate commerce by motor carrier;
(3)
the sale of passenger transportation in interstate commerce by motor carrier; or
(4)
the gross receipts derived from such transportation.
(Added Pub. L. 104–88, title I, § 103 , Dec. 29, 1995 , 109 Stat. 904 .)