TORONTO - Ontario is poised to become the latest province to penalize people for smoking in cars where children are present, but offenders will face much lighter fines than those originally proposed by the Liberal backbencher who first championed the widely-supported ban.

The province has already banned smoking in workplaces and public areas, such as bars and restaurants. Under the long-awaited legislation introduced Wednesday, the governing Liberals will also ban smoking in cars where children under the age of 16 are present -- a practice critics liken to child abuse.

Drivers and passengers who don't butt out while in a car with kids will be fined no more than $250, instead of between $200 to $1,000 that Liberal backbencher David Orazietti proposed in a private member's bill last year.

Premier Dalton McGuinty once dismissed a province-wide ban as a slippery slope which infringed too much on people's rights, but defended the bill Wednesday as a way of protecting kids from the dangers of second-hand smoke.

"We've got to take a side,'' he said. "And we're taking the side here of children who are defenceless and who count on us to make responsible decisions that serve their health interests.''

McGuinty announced his change of heart in March and threw his government's support behind Orazietti's bill, which gained widespread support from medical groups and anti-smoking activists.

Nova Scotia already bans the practice and British Columbia's Liberal government introduced a ban in its legislature earlier this week. New Brunswick and Prince Edward Island are also considering a similar ban.

Police will be expected to enforce the law once it takes effect, but the province is counting on a "high percentage of voluntary compliance,'' said Health Promotion Minister Margarett Best.

"The police will be out there doing their usual business and I'm certain that when they see the violation, then they will issue a ticket as required,'' she said.

The ban won't make the job more onerous for police officers patrolling the province's highways, who are already inspect things like child car seats, said OPP Const. David Woodford.

"If we happen to see someone in their car smoking and there's kids in the back seat, it's quite obvious,'' he said.

"We're not going to be out there just looking for that. We do all enforcement any time. But it wouldn't be hard to detect someone smoking in a car while there's kids in the car.''

But Woodford said he hasn't witnessed many people smoking in cars carrying children, unlike Best, who said she sees it "all the time.''

Opposition leaders agreed to support the ban Wednesday, but say more must be done to educate people about the dangers of exposing kids to high concentrations of second-hand smoke.

The law won't have much of an effect if people aren't made aware of what smoking does to their children's health, said Progressive Conservative Leader John Tory.

"We frankly have better things for the police and other people like that to be doing with their time,'' he said. "I think the way we're going to get change in behaviour here is by educating and informing and persuading people.''

Best said the province will "probably spend some money'' on educating the public, but will wait for the bill to be passed before moving ahead with any plans.

Two weeks ago, the Ontario Medical Association and the Heart and Stroke Foundation rolled out a series of radio and print ads encouraging parents to butt out while driving with kids.

The province says kids are exposed to up to 27 times the toxins when they're in enclosed spaces like a car, which can worsen asthma and lead to other respiratory illnesses.

Smokers' rights group Mychoice.ca has raised concerns that the ban will eventually extend to private homes, but McGuinty said he won't do that.