A new Apple Inc. iPhone 6s is seen atop its box at an Apple Store in Palo Alto, California, Sept. 25, 2015. David Paul Morris/Bloomberg via Getty Images

SAN FRANCISCO — Slumping revenue forecasts by key Apple suppliers in Asia could be a sign that the iPhone will soon see its first decline in annual sales since its debut in 2007. Recent forecasts released by Taiwan Semiconductor Manufacturing Co. and Largan Precision Co. Ltd, a camera lens producer, indicate that demand for parts used in the assembly of the iPhone are beginning to slow.

These lackluster forecasts add to recent worries that the iPhone's dominance may have finally run its course. Specifically, Taiwan Semiconductor Manufacturing this month forecast a year-to-year revenue drop of as much as 11 percent, which would be its steepest decline in almost seven years, according to Reuters.

iPhone Quarterly Sales Over Time | SpecOut

At the same time, Foxconn, the company responsible for assembling most iPhones, decided to cut working hours during the holiday season, according to Reuters. That period is supposed to be one of Apple and Foxconn's busiest times. Foxconn also saw its December revenues slump and missed its sales expectations for 2015.

"The pace of innovation has slowed. Apple is going toward the same direction as other brand names," a Taiwanese Apple supplier told Reuters.

Apple shareholders will not have long to wait to find out how the company is performing. The iPhone maker will release its latest quarterly earnings Tuesday.

Since the launch of the latest iPhone, Apple has seen its stock price fall nearly 15 percent, down from $119 in October to $101 on Friday. Over the same period, the Nasdaq index on which Apple trades has seen a slightly more modest decline of 11 percent. Apple is expected to release its next iPhone later this year.