The Carolina Panthers quarterback was fined $10,000 on Friday for wearing clips on his helmet visor featuring the Under Armour logo.
Although the clips that attach Newton's clear visor to the helmet are small and difficult to see, the league considers it a violation of its equipment policy.
NFL rules state that ''No visible identification of a manufacturer's name or logo on the exterior of a helmet or on any attachment to a helmet is permitted unless provided for under a commercial arrangement between the League and manufacturer.''
Nike has a signed contract to be the NFL's equipment provider. Newton is one of Under Armour's main clients.
The violation was first pointed in an article Tuesday by Forbes.com.