TORONTO -- A coalition of tobacco-control advocates is calling on the Ontario Film Review Board to toughen its rating for films that contain smoking-related scenes to keep young people from taking up the addictive habit.

The group wants the OFRB to designate any new movie that contains tobacco use as 18A, which would require anyone under age 18 to be accompanied by an adult. In the Maritimes and Manitoba, an 18A rating also means children under 14 are prohibited from viewing the film.

"In Ontario, 90 per cent of the top-grossing movies are all rated for children and teens," said Lorraine Fry, executive director of the Non-Smokers' Rights Association.

Movies now in theatres that contain smoking include "Paddington" (OFRB-rated G - suitable for all ages), "The Imitation Game" (PG - parental guidance), "Taken 3" and "Mortdecai" (both 14A - suitable for age 14 and up).

"This is one of the last forms of media where tobacco use can actually be shown to kids," said Fry, noting Canada has banned tobacco advertising and promotion.

"Actors are role models for kids and if they see a lot of smoking in movies by stars they look up to, then they're going to think it's cool, that it's socially acceptable, that it's a normal thing to do -- rather than something that kills half of its longtime users."

Fry said exceptions to the 18A rule for smoking content would include films depicting a historical character who smoked.

OFRB chair Bruce Davis said the government-appointed citizen panel considers content issues when rating a film like nudity, sexuality and violence. Since March 2013, the board has also required distributors include advisories noting specific content, including tobacco use.

Other provincial and regional review boards have their own rating criteria.

Davis said the board tries to strike a balance between a filmmakers' right of expression and the need to protect children.

"If someone came to us and said 'Any time there's drug use, alcohol use, reckless driving, tobacco use or inappropriate behaviour to women, we want all of those films to be 18A,' well virtually every film would be 18A," he said, adding those behaviours are part of culture.

Studies suggest exposure to smoking in movies is a major reason young people start lighting up.

Stanton Glantz, director of the Center for Tobacco Control Research and Education at the University of California, San Francisco, said research has found more than one-third of young people who take up smoking do so, at least in part, as a result of seeing characters in films puffing on cigarettes.

"The fundamental scientific data which is driving this is that exposure to on-screen smoking causes kids to smoke," Glantz said Tuesday.

"And there's a dose-response relationship: the more smoking kids see, the more likely they are to smoke," he said, explaining consistent results from studies around the world have shown "heavily exposed young people have twice or three times the risk of starting to smoke as do lightly exposed youth."

A study by the Ontario Tobacco Research Unit estimates in 2005 and 2007-2012, the years when data are available, more than 13,000 Ontario youth aged 12 to 17 took up the tobacco habit each year because of watching smoking in films.

The Canadian Tobacco, Alcohol and Drugs Survey released Tuesday shows the overall smoking rate among Canadians 15 and older is 15 per cent -- an all-time low. When it comes to youth, the survey found 11 per cent of teens 15 to 19 and 18 per cent of adults 20 to 24 report using tobacco.

Shoba John of India's Advocacy Forum for Tobacco Control said her country's government banned smoking in films and TV programs in 2005, but subsequent court rulings have watered down the legislation.

Still, there have been gains, said Mumbai-based John, special adviser to the HealthBridge Foundation of Canada.

Producers of films have to provide editorial justification for smoking in a film to India's certification board, along with disclaimers the actors don't endorse tobacco use at the start and midway through the film.

During scenes that depict tobacco use, a warning that smoking causes cancer or tobacco kills also must be shown.

"By and large they have been introduced as measures to deter producers from even thinking of (showing smoking) because no producer or director would want to have all those things in their movies."

In North America, Glantz said Canada may have a better chance of toughening ratings of movies with smoking content because review boards are provincial government agencies charged with protecting the public, while the U.S. rating system is voluntary and run by the movie studios.

Glantz and John will take part in a forum in Toronto on Thursday hosted by the Non-Smokers' Rights Association called Silencing Big Tobacco on the Big Screen, which will bring together representatives of public health agencies and youth organizations and tobacco control advocates.