Which of the following describes a direct violation of the Dormant Commerce Clause?

A direct violation of the Dormant Commerce Clause occurs when a state law discriminates against or unduly burdens interstate commerce. The Dormant Commerce Clause is a legal doctrine that is inferred from the Commerce Clause in the U.S. Constitution. It prevents states from enacting laws that favor their own businesses over out-of-state competitors, thereby ensuring that trade flows freely among the states.

In this context, a state law that benefits local industries at the expense of out-of-state businesses clearly exemplifies this violation. Such a law creates an unfair competitive advantage for in-state businesses and restricts market access for out-of-state businesses, thus impeding the free flow of commerce between states.

The other options do not constitute direct violations of the Dormant Commerce Clause. For instance, a rule ensuring environmental protection for all states may apply uniformly and does not discriminate against out-of-state commerce. A mutual agreement between states to regulate trade typically reflects cooperative federalism, which is permissible as long as it does not violate federal law or the Commerce Clause. A federal regulation mandating equal trade practices pertains to the federal government's authority to regulate interstate commerce, which does not infringe upon the Dormant Commerce Clause as it seeks to standardize practices rather than create discrimination.