Smoking would be banned in cars under plans being proposed by Labour.
Shadow health secretary Andy Burnham wants to introduce the measure in private cars to help protect children, who he says don't have a choice in inhaling toxic fumes.
The plan will be debated in the House of Lords on Wednesday but is expected to face opposition from peers who want to preserve the right to smoke in private places.
Labour banned smoking in public places in 2007, much to the anger of civil liberties groups.
Burnham campaigned last year for tougher measures on blank cigarette packaging.
He said: "Adults are free to make their own choices but that often does not apply to children and that's why society has an obligation to protect them from preventable harm."
The Leigh MP pointed to cars already being regulated environments, after the outlaw of using a mobile phone while driving and the requirement to use a seatbelt.
Secondhand smoke contains more than 4,000 chemicals, some of which are to blame for causing cancer.
It is particularly harmful for children, who have an increased risk of cot death, developing asthma and breathing conditions.
Children who grow up in with a parent or family member who smoke are three times more likely to start smoking themselves.
Professor Sheila Hollins, chair of the British Medical Association's Board of Science, backed the plans.
She said: "The BMA believes the proposed offence of failing to prevent smoking in private vehicles when children are present, is an important first step in reducing tobacco harm by restricting the prevalence of second hand smoke in private vehicles.
"Children are still developing physically and biologically and compared to adults they breathe more rapidly, absorb more pollutants and have less developed immune systems. As a result, they are more susceptible to the harmful effects of second hand smoke and are less likely to be able to choose to move away from it.
"Adults who smoke in the presence of children are not acting in the children's best interest; therefore it is the government's duty to change legislation in order to protect them."