Tim Cook, CEO, Apple Getty Images

At least four Apple suppliers have cut their revenue forecasts this week, fueling speculation that Apple is scaling back manufacturing of the iPhone. Apple said earlier this month it would stop reporting individual unit sales and revenue figures for the iPhone, leading some to speculate that the company has something to hide. Reports that its major suppliers are seeing reduced orders for electrical components could shed some light on expected sales. It's not the first time Apple has faced supply chain concerns — and none of the reports explicitly name Apple — but the number of reports is notable. Wall Street has certainly taken note, with several firms downgrading the stock this week and Apple's stock falling into bear market territory. Here are the Apple suppliers that have cut their forecasts so far:

AMS AG

Austria-based AMS AG makes sensors for 3D imaging, like the kind used in Apple's Face ID facial recognition system. The company said Thursday it was updating fourth-quarter revenue outlook "due to recent demand changes from a major consumer customer." AMS said it's seeing "increasing volatility in consumer customers' demand patterns ... which is not expected to decline." Shares of AMS rose 2 percent on Swiss exchanges Thursday.

Qorvo

Qorvo, a maker of radio frequency chips for use in smartphones and connected devices, cut its quarterly forecast Wednesday to a range of $800 million to $840 million, from a previously stated range of $880 million to $900 million. The company cited "recent demand changes for flagship smartphones." Shares of North Carolina-based Qorvo fell more than 1 percent Wednesday following the update, but made up some of those losses Thursday. The stock was up more than 1 percent in Thursday morning trading.

Lumentum

Lumentum, which makes 3D sensing lasers for the front-facing cameras of Apple iPhones, reduced its revenue outlook Monday by $70 million at the low end. Lumentum CEO Alan Lowe said one of its largest customers issued a request to "materially reduce shipments to them during our fiscal second quarter." Lumentum listed Apple as its largest customer in its 2018 annual filing and said the iPhone maker accounts for 30 percent of Lumentum's revenue. Monday's update sent Apple shares tumbling and sent Lumentum shares plunging more than 30 percent.

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