The Welsh Assemble is to vote today on whether smoking in cars with children present should be banned.
Should the law be approved, drivers caught lighting-up in the presence of passengers under 18 years old would face a £50 fixed penalty from October.
Like the rest of the United Kingdom, smoking in work and public service vehicles is already prohibited under legislation passed in 2007, as they are designated as indoor public places.
The new measures are aimed at reducing the well-documented harm caused by second-hand smoke, to those who have no choice but to be subjected to it.
Health Minister Mark Drakeford said smoke posed "a real and substantial threat to children's health,” the BBC reports.
"Children cannot escape from the toxic chemicals contained in second-hand smoke when travelling in cars. They often don't have a choice over whether or not they travel in cars and may not feel able to ask an adult to stop smoking.”
He added: "As with the existing smoke-free regulations, success will not be based on the number of enforcement actions that are taken but by how behaviour, attitudes and health outcomes change over time."
A similar ban has already been approved in England, and is due to come into effect on October 1. Drivers with no passengers, or those in convertible cars with the roof down are not subject to the restriction. The move was welcomed by health charities, though smokers’ group Forest claimed the ban would be unenforceable.