The Maryland Senate is debating a bill that would ban smoking in vehicles with passengers who are younger than 8.

On Friday, legislators amended the bill to change the age at which a child cannot be exposed to smoking in a car to 16 and younger, but the amendment was overturned. Supporters of the bill said that while breathing in secondhand smoke is harmful to children of all ages, the law would be easier to enforce if it focused on young children, according to the Associated Press. Police officers will know if a child is under 8, because until that age, children must ride in car seats, the article notes.

According to Action on Smoking and Health, at least five U.S. states—Arkansas, California, Louisiana, Maine and Oregon—have banned smoking in cars when children are present.

More than one-fifth of middle and high school students were exposed to secondhand smoke in cars in 2009, according to a recent study by the Centers for Disease Control and Prevention. This represents a significant decrease from 2000, when 40 percent of teens were exposed to cigarette smoke in cars.