Carolina Panthers quarterback Cam Newton was fined $10,000 by the NFL on Friday for using unapproved Under Armour visor clips on his helmet.
The small, black clips with the logo blacked out violate the league's equipment policy.
"No invisible 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," the rule states.
Forbes revealed the violation on Tuesday in an article that featured pictures of Newton's helmet with the clips. Newton and New England Patriots quarterback Tom Brady are two of Under Armour's most prominent clients. Under Armour pays Newton more than $1 million per year, according to Forbes.
Nike pays $1.1 billion to be the NFL's official apparel partner through 2016.