Supplies for the higher-end iPhone are said to be constrained at launch Friday, according to Boy Genius Report and 9to5 Mac. The carriers also are reportedly facing supply issues, according to AllThingsD.
One carrier source backed up the report to CNET.
"We don't believe we'll have inventory of the iPhone 5S to satisfy demand," said a person familiar with one of the major carrier's launch plans. "We would certainly like more. Hopefully (Apple) will resupply quickly."
Supply issues aren't new to Apple. Indeed, the company often faces shortages with each new iPhone.
It's unclear why there's an issue with the iPhone 5S inventory. But some had already feared a scarcity of supply when Apple only offered the iPhone 5C for preorder. Anyone who wants the iPhone 5S on the first day will have to go to a carrier or Apple store.
CNET contacted Apple for comment, and we'll update the story when the company responds. Verizon Wireless and AT&T declined to comment, while Sprint and T-Mobile weren't immediately available for comment.
This is the first year Apple is offering two new iPhones, having previously discounted older versions of its flagship phone as the low-cost option. But with the iPhone 5C, the company is offering a plastic version of the iPhone 5, alongside the option for different colors.
Appleearlier Tuesday to fans looking to buy either iPhone. In it, the company noted that the phones would be available at its stores, carriers, and retail partners.
In the past, Apple has doled out a certain part of its inventory to the carriers and retailers, but the best bet for getting a new iPhone was to go to an Apple store. But this year, it may be tough to get an iPhone 5S no matter where you go.
Check back in on Friday for CNET's coverage of iPhone launch day.
Updated at 1:04 p.m. PT: to include a comment from a carrier source.