Cars could be added to the ever-shrinking sphere where Minnesotans are allowed to light up.

A bill introduced Thursday in the Legislature would ban smoking in cars where children are riding.

It would be the latest expansion of prohibitions on smoking that began in 1975, when Minnesota became the first state to ban smoking in most workplaces.

And the bill's House author, Rep. Nora Slawik, is bracing for a fight that could reprise the battle over the 2007 Freedom to Breathe Act, which banned smoking in bars and restaurants.

But she said her goal -- what she called "a generation of healthier kids" -- should override any objections.

The bill would make it illegal to smoke in cars while driving with passengers younger than 18, treating it as a moving violation. That would carry a $100 fine. But it would be considered a secondary offense, akin to not wearing a seat belt; a driver would have to be stopped for some other offense before being ticketed for smoking.

Slawik said she came up with the idea for the ban while being interviewed last year by a constituent who was researching public policy issues related to secondhand smoke. The constituent mentioned the fact that at least four other states have banned smoking while driving with children.

She also discovered that the activists who pushed the Freedom to Breathe Act were considering pushing such a ban, "so I'll have some support on this." Slawik said a companion bill will be introduced in the Senate, probably next week, by Sen. Sandy Pappas, DFL-St. Paul.