The correct answer to this open question is the following.
Suppose the state of Georgia enacts a law requiring all trucks to remove rear-fender mudguards on trucks while they pass through any interstate roads in Georgia. The United States trucking Association sues the state of Georgia. The legal theory they will use is the Commerce Clause, cited in Article 1, Section 8, Clause 3 of the Constitution of the United States. Here, it is said that the US Congress has the power to regulate interstate trade and trade with other countries. Because it is the US Congrees that regulates commercial activities and not the states, in this case, the state of Georgia, the United States Trucking Association has good chances of winning the case. Probably the state law would violate federal law because it restricts trade.