GENEVA — The Swatch Group may be best known for its playful, plastic watches. But it also produces mechanical movements and other watch components that it sells to most of its rival timepiece makers.

Starting Jan. 1, though, the company will begin to cut back, and possibly eventually end, its sales of the inner workings to competitors to concentrate on producing watches with higher profit margins and to make sure it has enough supplies on hand for its own brands, including Longines, Omega, Tissot and Breguet.

Swatch’s move, which was approved by Switzerland’s competition authority, is being challenged in court by nine watch companies, many of them small and without the financial wherewithal to produce their own movements.

The plaintiffs predict that several companies will disappear because they have few other options for the parts, which must come from Switzerland to keep the lucrative “Swiss made” label. They also argue that if Swatch goes through with its withdrawal, the result could be as wrenching to the Swiss watch industry as the arrival of Japanese digital watches, which almost led to the industry’s collapse in the 1970s.