Final answer:
The Supreme Court case relevant to Maine's law against Idaho potato shipments is Gibbons v. Ogden, which established that interstate commerce is under the control of Congress, not individual states.
Step-by-step explanation:
In the context of Maine passing a law to prevent the shipping of Idaho potatoes to Maine supermarkets, the most applicable Supreme Court case is Gibbons v. Ogden (1824).
This landmark decision addressed the scope of the federal government's power under the Commerce Clause of the Constitution. In Gibbons v. Ogden, the Supreme Court ruled that the state of New York could not grant a monopoly on waterborne trade between New York and New Jersey, as this was a matter of interstate commerce which fell under the purview of Congress. This precedent is relevant to the situation with Maine because it implies that individual states do not have the authority to restrict interstate commerce, as in the transportation of goods (like potatoes) from one state to another.