The company says a "limited number" of users have reported skin problems. It says that may be from an allergy to the nickel used in the Force.
The Force, which was released in October, can track steps taken, stairs climbed and calories burned. FitBit also makes other fitness wristbands and devices.
One online company forum began showing user complaints in mid-December and has grown to more than 30 pages.
Fitbit said late Tuesday that it is looking at ways to modify the wristband so that anyone can wear it comfortably.
The issue was first reported Monday by online news site Consumerist.
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