Smokers have already been banned from New York bars and restaurants, and soon they could be prohibited from lighting up in cars carrying minors, an idea giving added fuel to critics who say the city has become a nanny state.

A City Council member of Queens who is chairman of the council's Environmental Protection Committee, James Gennaro, said he is planning to introduce the smoking bill next week.

"I am just seeking every opportunity I can to denormalize smoking and to try to put it out of the reach of kids," Mr. Gennaro said. "I've lost family members to lung cancer and I've seen what happens."

If enacted, smoking in cars with riders under the age of 18 would join a growing list of activities barred by the city, including making too much noise at night, serving trans fats in restaurants, and allowing students to carry cell phones in school.

Mayor Bloomberg, who has spearheaded worldwide anti-tobacco initiatives, used the health risks associated with second-hand smoke to argue for a ban on smoking in bars.

A spokesman for Mr. Bloomberg, Stuart Loeser, declined to comment, saying the mayor had not yet seen the bill.

When asked in January about a similar proposal in Rockland County, Mr. Bloomberg said people should have the right to smoke in their own cars, but "if it's a child in the car, who doesn't have the ability to speak up and protect themselves, then society does start to have an interest."

While he admitted he didn't know how such a proposal would be enforced, the mayor said, "We do have a responsibility to provide a health environment for our children and I would just urge anybody, if you have children at home, don't smoke at home, don't smoke in your car with your child; you really are damaging your child's health."

Mr. Gennaro's proposal calls for fines of $200 to $400 for a first smoking violation, $500 to $1,000 for a second violation in a single year, and between $1,000 and $2,000 for a third violation in a year. The New York Police Department would get the task of enforcing the law.

In Rockland County, which in June approved a measure to ban smoking in cars with minors, critics called the law an invasion of privacy and a violation of personal liberties. Mr. Gennaro dismissed those arguments.

"Boo-hoo," he said. "You can't subject kids to 43 carcinogens and 250 poisonous chemicals and claim privacy. Get over it. Their right to privacy doesn't extend so far as to poisoning kids."

A child who spends one hour in a very smoky room is inhaling as many dangerous chemicals as if he or she smoked 10 or more cigarettes, according to the Mayo Clinic.

A U.S. Surgeon General's report from 2006 found there is sufficient evidence to infer "a causal relationship" between secondhand smoke exposure from parental smoking and lower respiratory illnesses in infants and children.

The founder of Citizens Lobbying Against Smoker Harassment, Audrey Silk, said the proposal is an example of government overreach and should be considered part of an alarming trend that affects smokers and nonsmokers alike.

"Smoking bans are a symptom of a greater problem with our government, that they can come in and regulate all kinds of lifestyle choices because they've deemed it improper," she said. "It could be anything."

A lawyer and former executive director of the New York Civil Liberties Union, Norman Siegel, said the proposal is "very intrusive," and noted that to withstand judicial challenges, at a minimum the city would have to show that second-hand smoke in cars has a negative health effect of minors.

The Rockland County legislator who sponsored the county's bill on smoking in cars, Connie Coker, said there's no reason why the government shouldn't be able regulate smoking in cars, as it already regulates cell phone use while driving and requires car seats for young children.

"It's not your castle," she said. "Your car is out in the world."

Ms. Silk said that if the bill were approved, there would be no reason the government wouldn't try to regulate the number of cookies parents could give their children.

"If they can come into our car, then they can come into our home," she said. "And everybody should be afraid of this, not just because of smoking."