Though Apple has trumpeted its services segment as a potential hedge against slowing iPhone sales, one of the top analysts believes the company is facing a growing revolt against the transaction fees it charges for apps.

"While the services segment grew 18 percent in the December quarter, we've now started to get investor questions worrying about whether the App Store will be the next shoe to drop," AB Bernstein's Toni Sacconaghi wrote in a note Friday. "Certainly, the headlines in the last few months haven't been encouraging. Netflix, Spotify, and Fortnite have all stopped / threatened to stop paying the so-called 'Apple Tax' of 15 to 30 percent on App Store revenues."