Ontario is following in the footsteps of other provinces across Canada in pursuing a ban on smoking in vehicles where children are present.

Premier Dalton McGuinty was initially against the idea, saying it infringed on people's rights, but did an about-face on Wednesday when he announced his government would propose the new law this spring.

McGuinty said he changed his mind after listening to medical experts, those within his party and residents on the street.

"Those Ontarians are right and I was initially wrong, and so we're going to do what is right," he said.

"We're going to do something that speaks to the value we attach to our most vulnerable segment in our society -- our children."

The premier said one hour of second-hand smoke in a car "is the same as giving kids an entire pack of cigarettes.''

Nova Scotia has a ban and the British Columbia government promised one in its recent throne speech. Manitoba and New Brunswick are both considering a similar law.

Last year, McGuinty shied away from the idea, but last week said he was reconsidering the proposal due to intense lobbying by his minister of health promotion and Liberal backbencher David Orazietti, who introduced a private member's bill that would ban the practice.

Orazietti's bill suggests a maximum $200 fine for infractions where an adult is found smoking in a vehicle where a child under the age of 16 is present.

"Eighty per cent of all Ontarians favour legislation to protect children in an automobile from second-hand smoke," he said on Wednesday.

The proposed ban is supported by medical groups and anti-smoking activists, including the Ontario Medical Association and the Heart and Stroke Foundation.

OMA president Dr. Janice Willett said children are exposed to up to 23 times the toxins when they're in enclosed spaces like a car, which can worsen asthma and lead to other respiratory illnesses.

"It's bad, it's the worst possible environment," said OMA chairwoman Suzanne Strasberg. "The concentration of smoke in cars is 60 per cent higher than in a house."

Second-hand smoke kills

Tobacco use is the number one cause of preventable disease and death in Ontario, killing more than 13,000 Ontarians every year, the government says. Second-hand smoke kills more than 300 Ontario residents annually, and tobacco-related diseases directly cost Ontario's health care system $1.6 billion a year.

In response to McGuinty's policy reversal, opposition critics said the premier changed his tune to please constituents.

"I think the polls must have been overwhelmingly in favour of this,'' said NDP critic Michael Prue.

"I can't imagine any other reason .... They've seen that people support this, and notwithstanding his reticence, he's figured that it's a popular thing to do.''

McGuinty hopes all parties in the legislature will back the proposed new law during the spring session, which is scheduled to begin March 17.

He said he has no plans to ban smoking in private homes where kids are present.

"You've got to continually look to ensure that you're striking the appropriate balance between the rights of individuals -- the right to exercise personal freedoms and liberties -- and our collective responsibility as a society to protect the interests of our most vulnerable,'' McGuinty said.

With a report from CTV Toronto's Paul Bliss and files from The Canadian Press