Apple shares have tumbled into the red after reports that the Supreme Court sounds open to allowing a lawsuit to go forward that claims Apple has unfairly monopolized the market for the sale of iPhone apps.

As AP reports, the court has heard arguments in Apple's effort to shut down an antitrust lawsuit.

Chief Justice John Roberts was alone among the nine justices in seeming ready to agree with Apple.

The suit by iPhone users could force Apple to cut the 30 percent commission it charges software developers whose apps are sold exclusively through Apple's App Store.

A judge could triple the compensation to consumers under antitrust law if Apple ultimately loses the suit.

Justice Stephen Breyer used to teach antitrust law at Harvard Law School. He says the consumers' case seemed straightforward.

Apple argues it's merely a pipeline between app developers and consumers.

And the drop in AAPL has weighed on the broad US equity markets...

And while stocks are still positive, selling pressure is not-stop and increasing...