In its defense, Apple said the company plays no role in setting an app's price; that decision is up to the app's developer.
The Justice Department is supporting Apple, although Solicitor General Noel Francisco acknowledged that Apple exploits its powerful position in the market by imposing the 30 percent commission.
Justice Brett Kavanaugh said consumers experience harm through higher prices, but also noted that plaintiffs' basis to sue is murky, because Apple doesn't purchase apps from developers and then resell them to consumers. "From my perspective, I've just engaged in a one-step transaction with Apple", Kagan said. Today, the two parties will argue whether or not consumers are entitled to damages in antitrust cases, even when the goods were sold by third parties who actually set the prices.
The case of Apple v. Pepper narrowly avoided being thrown out because existing antitrust laws may only apply to the App Store if consumers are considered direct purchasers.
Software developers say that outcome would disrupt similar online marketplaces that operate between app creators and customers. Under this "shopping mall" theory, a shopper can not sue the owner of the mall by asserting he or she paid too much for a product at a store.
"The plaintiffs, as well as antitrust watchdog groups, said closing courthouse doors to those who buy end products would undermine antitrust enforcement and allow monopolistic behavior to expand unchecked".
An Apple spokesperson said in a statement to Fortune that the App Store "has fueled competition and growth in app development", which created millions of jobs and resulted in over $100 billion in payments to developments worldwide.
In an hour-long oral argument session this morning, though, some justices seemed to take a skeptical line.
"Apple is a sales and distribution agent for developers", Apple's lawyers said in a Supreme Court filing.
The suit by iPhone users could force Apple to cut the 30 percent commission it charges software developers whose apps are sold through the App Store. Part of the concern, the court said in that case, was to free judges from having to make complex calculations of damages.
The Trump administration is siding with Apple.
But Apple's critics say its control over the App Store makes it unlike other internet marketplaces. A judge could triple the compensation to consumers under antitrust law if Apple ultimately loses the suit.
He is representing a group of consumers, led by Chicagoan Robert Pepper, that wants to show app prices would be lower if not for Apple's actions. A ruling is expected to come by June at the latest.