The Macon Grocery Company v. Atlantic Coast Line Railroad Company case in 1909 revolved around the issue of freight rates and their regulation by state authorities versus federal ones. The Macon Grocery Co., a Georgia-based company, sued the Atlantic Coast Line Railroad for charging higher freight rates on intrastate shipments than interstate ones, which they claimed was discriminatory and violated Georgia law. However, the railroad argued that its rates were set according to regulations established by the Interstate Commerce Commission (ICC), a federal body. The Supreme Court ruled in favor of the railroad company, stating that when there is conflict between state and federal regulations concerning commerce matters such as this one, federal law prevails under the Supremacy Clause of U.S Constitution. This decision reinforced ICC's authority over railroads' rate-setting practices.

In the dissenting opinion for Macon Grocery Company v. Atlantic Coast Line Railroad Company, it was argued that the majority's decision failed to properly consider and apply principles of equity. The dissenting justices contended that the railroad company had not acted unfairly or unjustly in its dealings with Macon Grocery Company, as they believed there was no evidence of discriminatory practices on part of the railroad company. They also disagreed with the majority's interpretation and application of Interstate Commerce Act provisions, arguing that these were misapplied by failing to take into account whether any alleged discrimination caused actual harm or injury to competition. Furthermore, they expressed concern about potential negative implications this ruling could have on future cases involving similar circumstances - particularly those related to rate regulation issues within transportation industries - warning it might set a dangerous precedent which could unduly burden businesses without providing clear benefits for consumers or promoting fair competition.