§ 453. “A State may Levy.”
Sec. 90 provides that after uniform duties have been imposed, the power of the Parliament to impose duties of customs shall be exclusive. That section accordingly prohibits the States from thereafter imposing duties of customs — a term which includes both import and export duties on goods entering or leaving the Commonwealth. (Webster's Internat. Dict.) Sec. 92 further provides that from the same time “trade, commerce, and intercourse among the States … shall be absolutely free.” That section prohibits the States and the Commonwealth from imposing duties on goods passing from one State to another.
This section reserves to the States, notwithstanding the above provisions, the police power of making charges which may be necessary for executing their inspection laws. Such charges would seem to be both taxes and duties, and might, in the absence of special provision, have been held to be within either or both of the above prohibitions.
The section, however, though it expressly reserves this police power to the States, also makes the exercise of the power subject to control by the Federal Parliament. State laws imposing such charges, even though they may be necessary for executing the inspection laws of the State, may be annulled by the Federal Parliament; and if they are not necessary for that purpose, they are not protected from the prohibitions of secs. 90 and 92.