Foxconn and a number of Apple's vendors have pointed toward lower December revenue in 2015. Reuters/Pichi Chuang

One of Apple’s key iPhone assemblers took a beating during the busy holiday month. Hon Hai Precision Industry Co., commonly known as Foxconn, saw its revenue in December fall by 20 percent, according to Reuters.

The company reported revenue for the month of 409.65 billion New Taiwan dollars ($12.3 billion) down from 515.57 billion New Taiwan dollars ($15.5 billion) in 2014. While revenue for the entire year was up 6.4 percent to 4.48 trillion New Taiwan dollars, it was slightly below the 7 percent gain expected by analysts polled by Thomson Reuters.

Foxconn is also expected to cut workers’ hours over the weeklong Lunar New Year holiday, which begins Feb. 8. It’s the latest flag raised by suppliers warning of what could be a rough 2016 for Apple.

Several supply chain vendors are also expected to reduce output of parts for the latest iPhones by around 30 percent, according to Nikkei. The reduced output is expected to help dealers clear out excess inventory of the iPhone 6S and 6S Plus.

Apple vendors such as Japan Display, Sharp, LG Display and Sony are also expected to be hit by the reduced orders. Apple suppliers Cirrus Logic and Qorvo Thursday also warned about potential revenue shortfalls for the holiday quarter, according to Reuters.

Several analysts have lowered their estimates for iPhone sales in response to the signals from Apple’s supply chain. Michael Walkley, a Wall Street analyst at Canaccord Genuity, lowered his 2016 iPhone sales estimates to 219 million units, down from his previous estimate of 231 million, according to a research note released Friday.

His estimate, along with estimates from Morgan Stanley’s Katy Huberty, point to a potential year-over-year sales decline for Apple’s iPhone, a first for the company’s flagship product, which accounted for $155 billion in sales, nearly two thirds of Apple’s revenue, last year.