Am. Trucking Associations, Inc. v. Scheiner
In Am. Trucking Associations, Inc. v. Scheiner, 483 U.S. 266 (1987), applying Commerce Clause principals, the Supreme Court struck down two Pennsylvania flat taxes; one a marker fee for motor carrier vehicles (These were defined as a "truck, truck tractor or combination having a gross weight or registered gross weight in excess of 17,000 pounds." and one an axle tax. (Applicable to "truck, truck tractor or combinations weighing more than 26,000 pounds).
These flat taxes applied to all applicable vehicles, whether registered in Pennsylvania or not. The Court recognized two distinct challenges raised.
The first argument, not applicable here, was to the tax statutes' provisions that both "deemed" Pennsylvania registered vehicles to have paid the marker fee and also offset the axle tax charge with an equivalent reduction.
Although such argument weighed heavily in the lower courts, it did not in the Scheiner decision. Instead, the Scheiner Court's decision was based primarily on the second argument raised: that the flat taxes were "discriminatory because both taxes imposed a much heavier charge per mile of highway usage by out-of-state vehicles." (Id. at 276).
The Scheiner decision was premised on the actual impact the taxes had on intrastate and interstate vehicles.
Driven by factual findings, the Court stated "in practical effect, since the challenged flat taxes impose a cost per mile on out-of-state trucks that is approximately five times as heavy as the cost per mile borne by local trucks, the taxes are plainly discriminatory." (Id. at 286).