Apple has already begun accepting pre-orders for its new iPhone 6s and iPhone 6s Plus, but the company is not expected to complete shipments for another month after its announced shipment date of September 25.

The issue appears to have been caused by bottlenecks down the production line, according to KGI Securities analyst Ming-Chi Kuo, who says that shipping times for the iPhone 6s Plus that have already been pre-ordered could be extended by three to four weeks past their expected date of shipment.

In a research note sent to clients that was obtained by 9to5Mac, Kuo says the problem seems to lie with Minebea, Apple's Japanese supplier of backlight. Kuo says Apple has already placed rushed orders with another supplier, Radiant, which apparently has more experience in providing backlight components for Cupertino, as it also supplies backlight for the 7.9-inch iPad mini.

"We believe Radiant is receiving rush orders, because Minebea is having production issues," said Kuo. "This tells us that Radiant is more skilled at producing backlight module for 6S Plus given its accumulated abundant experience supplying the backlight module for iPad mini (a similar size to iPad). To accelerate availability, we believe Apple has been transferring substantial 6S Plus backlight module orders to Radiant."

That said, Kuo thinks Apple will increase its orders for backlight modules from Radiant by 70 to 80 percent, from 35 to 45 percent. He also believes Apple is on track to to have anywhere between 1.5 million and 2.5 million iPhone units available for shipment on September 25.

On Monday, Apple CEO Tim Cook announced that pre-orders for the iPhone 6s and iPhone 6s Plus have already exceeded the pre-order numbers for the iPhone 6 and iPhone 6 Plus. The firm is looking to break its own record of selling 10 million iPhones during its launch weekend — a feat that is not impossible, considering the devices will be available at launch in China, the biggest and hottest new market for the technology industry.

Aside from the United States and China, the iPhone 6s and iPhone 6s Plus will also debut in Canada, the United Kingdom, France, Germany, Japan, Hong Kong, New Zealand, Singapore and Puerto Rico on September 25. Will we be seeing long lines at the Apple Store once again? It won't be long until we find out.