Neither driver could be reached for comment.
It was reported earlier this week by The Associated Press that two star Cup drivers were fined, one as much as $50,000, for critical comments about the sport. NASCAR officials declined to name the drivers, but defended their right to maintain some sense of control for the sake of the brand.
"It is the sanctioning body's obligation on behalf of the industry and our fans to protect the sport's brand," spokesman Ramsey Poston said in a statement. "Any action taken by NASCAR has nothing to do with the drivers expressing an opinion -- it's focused on actions or comments that materially damage the sport.
"We have specifically discussed this in meetings with teams, drivers and stakeholders."
Newman was fined first and Hamlin second, the sources said. The sources would not confirm which statements made by the drivers were responsible for the fines, but both drivers have been outspoken on several issues.
David Newton covers NASCAR for ESPN.com.