TORONTO -- A proposed Ontario law that would demand zero blood alcohol levels for all motorists 21 and under and limit the number of passengers in the vehicle would also get tough on people of all ages who drive with a suspended licence, The Canadian Press has learned.

Sources said the legislation, to be introduced Tuesday, would go after people who still drive despite having had their licences suspended for drunk driving by immediately impounding their vehicle for seven days.

A vehicle would also be seized for seven days if someone who has been ordered by the courts to install an ignition locking device that tests the driver for alcohol is pulled over in someone else's car.

Heavy habitual drinkers who ignore the laws and licence suspensions must be dealt with, said Prof. Robert Solomon of the University of Western Ontario, a national director of Mothers Against Drunk Driving.

"These are guys who have a drinking problem and if you don't address it, they're going to rack up a number of crashes," he warned.

The zero blood alcohol limit for Ontario drivers aged 16 to 21 would apply even to those who have enough experience behind the wheel to move up from the more restrictive graduated licences to a regular driver's licence.

"There is a wealth of research indicating that zero blood alcohol content limits until you reach the age of 21 significantly reduce deaths and injuries among young drivers," said Solomon.

"Those between 16 and 25 represent 13.7 per cent of the population, but 32.1 per cent of the alcohol-related traffic deaths. Impaired driving remains the number one criminal cause of death in our country."

New Brunswick passed legislation with a zero tolerance for alcohol for drivers 21 and under earlier this year, while Manitoba and Nova Scotia have similar no alcohol rules for the first five years for all new drivers, regardless of age.

Under the new bill, teenage drivers in Ontario would only be allowed one passenger aged 16 to 19 -- although there would be exemptions for brothers and sisters. Studies show just one teenage passenger with a teen driver doubles the chances of an accident.

That risk increases with the addition of every teenage passenger, according to the Insurance Institute for Highway Safety.

New drivers in Ontario are currently allowed as many passengers as they want during the day, but for the first six months of their G2 graduated licence they can't have more than one person under 19 in the vehicle from midnight until 5 a.m.

Under the proposed legislation, young Ontario drivers caught speeding would face a series of escalating sanctions, starting with a 30-day licence suspension. That grows to 90 days for a second offence and to a total suspension for a third offence. The person would then have to start over with beginner's driver training courses and apply for a new licence.

"Three strikes and you're out," said the government source.

People who continue to drive despite having had their licenses suspended for outstanding traffic tickets or for medical reasons would not be subjected to the automatic impounding of their vehicles, said the source.

That's because drivers who had their licence suspended for not paying tickets won't be able to renew their vehicle permits until they are paid, and sometimes there's a lag behind the returning of a licence that had been suspended for medical reasons and the actual paperwork.

"The people we're targeting are people who have been charged with driving under the influence and are driving with a suspended licence," said the source. "We want to go after people where there's pretty hard evidence that you're breaking the law."

Until recently, Premier Dalton McGuinty rejected calls to ban young drivers from drinking alcohol, suggesting it was something better left to parents than to a provincial law. He changed his mind after lobbying by the father of one of three young men killed in an accident last summer.

Tim Mulcahy campaigned publicly for changes to the drinking and driving laws after his son Tyler, and two young friends, died in a crash in Muskoka after they had been drinking, taking out full page ads in newspapers urging McGuinty to "make a difference and reduce future suffering."

Mothers Against Drunk Driving, which has been campaigning for laws to stop young drivers under 21 from drinking, said it was "very pleased" with the Ontario legislation but saddened that it took a tragedy to prompt government action.