The small, black clips with the logo blacked out, according to league policy, violated the NFL's equipment policy.
According to the rulebook, "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 violation was revealed in a Forbes.com article Tuesday 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 high-profile clients. According to the Forbes.com article, Under Armour gave Newton a deal that would pay him more than $1 million annually when he was the top pick of the 2011 draft.
Nike reportedly pays $1.1 billion to be the league's apparel partner through 2016.
Other players who have worn the clips are Oakland Raiders quarterback Terrelle Pryor, San Francisco 49ers safety Eric Reid and Cleveland Browns receiver Josh Gordon, according to Forbes.com. The Charlotte Observer reported that at least three other Panthers -- defensive ends Greg Hardy and Charles Johnson and running back DeAngelo Williams -- have worn the Under Armour clips. A source, however, said they were not fined because the black clips were on black face masks; Newton's were more noticeable because they were black clips on a gray face mask.
In other fines handed down by the league Friday:
• Steelers wide receiver Antonio Brown received $15,750 in fines for two unnecessary roughness violations: $7,875 for a late hit on Bears safety Chris Conte and $7,875 for a face mask on Chicago's Sherrick McManis.
• Titans LB Moise Fokou has been docked $7,875 for unnecessary roughness for a face mask violation.
• Lions defensive tackle Nick Fairley was fined $10,000 for a personal foul during Sunday's win against the Redskins. The foul came on a play where Detroit rookie defensive end Ziggy Ansah sacked Washington quarterback Robert Griffin III, forcing a fumble.
Information from ESPN.com's David Newton and Michael Rothstein, ESPN NFL Insider Ed Werder and The Associated Press was used in this report.