The city council approved the controversial measure in a 6-3 vote last month, drawing a mixed response from residents, with some saying it infringes on individual freedom and others welcoming the move.
The ordinance prohibits adults from smoking in vehicles in which children under the age of 18 are present. Violators will be fined 50 dollars.
Similar anti-smoking measures have been adopted in Arkansas and Louisiana. Those measures, however, target adults smoking in the presence of children under the age of six or eight.
Bangor Police Chief Don Winslow told AFP that his officers would take a flexible approach in enforcing the smoking ordinance, issuing warnings the first few months rather than fines.
"We're not going to go out and aggressively try to find people in violation, but as we come across people that are smoking with a child present we'll use the opportunity to educate them," he said.
"We're not out there to see how many tickets we can write, we look for voluntary compliance."
Several other US states and cities are considering adopting similar anti-smoking bans.