Hollywood's Jack Valenti has rejected a proposal that would see films that feature smoking carry an adult rating.
Chicago was singled out for criticism in a recent report on smoking in films
Mr Valenti, head of the Motion Picture Association of America, told the US Senate the film industry opposed any restrictions to their artistic freedom.
"Film-makers must decide what story to tell and how to tell it," he said.
Valenti, who devised the ratings system in 1968, rejected any proposed changes: "I want to make sure this rating system does not get cluttered up," he said.
The industry is facing political pressure, following research last year which suggested teenagers who watched smoking on screen were more likely to take up the habit.
A further report in March, issued by the University of California, suggested smoking should be treated in the same way as swearing.
Professor Stanton Glantz called on films such as Seabiscuit and Chicago to be given adult ratings because they include smoking.
"Why is it OK to modify [films] for nudity, for language, but it's not OK to modify it for tobacco - the number one preventable health problem we have in this country?" asked Senator John Ensign, a Nevada Republican during a Commerce Committee hearing on Tuesday.
In principle, Mr Valenti agreed he was against smoking being shown gratuitously on screen, and in favour of preceding movies with public service announcements warning about the dangers of smoking.
But he also insisted smoking was sometimes integral to portraying real life on film.
One study linked smoking on screen to teens taking up the habit
Mr Valenti added that changes to the ratings system would prompt similar demands from groups concerned about issues like alcohol abuse and animal cruelty.
"I want to make sure this rating system does not get cluttered up with a bunch of other people who have equally passionate views that want to be included," he said.
"I've lived this for 38 years and I understand it very well."
However, Congress has threatened to become more aggressive on the issue if the US film industry continues to do nothing to address its concerns