In the case of Marshall Dental Manufacturing Company v. State of Iowa, 1912, the U.S Supreme Court was tasked with determining whether a state law that prohibited dental supply companies from employing or contracting licensed dentists to perform dental procedures violated the Fourteenth Amendment's Due Process and Equal Protection Clauses. The plaintiff, Marshall Dental Manufacturing Company, argued that this law unfairly restricted their business practices and infringed upon their constitutional rights. However, the court ruled in favor of Iowa stating that states have broad powers to regulate businesses within their borders for public health reasons under its police power authority. The court found no violation of either due process or equal protection as it deemed such regulation reasonable and not arbitrary nor discriminatory against any particular class but rather aimed at protecting public welfare by ensuring only qualified individuals practiced dentistry.

The dissenting opinion in the case of Marshall Dental Manufacturing Company v. State of Iowa argued that the state's regulation, which prohibited out-of-state dental supply companies from selling directly to dentists without first obtaining a license and establishing a place of business within the state, was unconstitutional. The justice contended that this law violated both the Due Process Clause and Commerce Clause of the Constitution by unduly burdening interstate commerce and denying equal protection under law for non-resident businesses. They believed it was an unfair trade practice designed to protect local dealers at expense of outside competitors, thus creating monopoly-like conditions contrary to free market principles. Furthermore, they asserted that such restrictions could lead other states to enact similar laws thereby disrupting national economic unity.