Driver Denny Hamlin received a $25,000 fine Thursday for critical remarks about the new Gen-6 race car.
Hamlin's comments, made after last week's race at Phoenix, were deemed harmful to stock car racing by its governing body.
While drivers get "ample leeway in voicing their opinions when it comes to a wide range of aspects about the sport, the sanctioning body will not tolerate publicly made comments by its drivers that denigrate the racing product," NASCAR said.
After a third-place finish Sunday in the second race for NASCAR's new Gen-6 race car, Hamlin responded to a question about how he liked the vehicle. He said: "I don't want to be the pessimist, but it did not race as good as our generation five cars. This is more like what the generation five was at the beginning."