Andrea Scott says she would never throw a candy wrapper on the ground.

“Littering is one of my pet peeves, and I always told my kids they’d be in big trouble if I catch them doing it,” said Ms. Scott, a 43-year-old financial executive, as she sat outside an office tower on Michigan Avenue in Chicago on a recent sunny afternoon. “I see people throw stuff out their car windows, and I cringe.”

Yet she confesses that she routinely discards cigarette butts on the sidewalk.

For her and countless other American smokers, cigarette butts are an exception to the no-littering rule. “Aren’t cigarettes biodegradable?” volunteered Libby Moustakas, a co-worker who was enjoying a smoking break with Ms. Scott.

But dozens of municipalities across the nation have had enough. Weary of the butts’ unsightliness and the costs of sweeping them up, cities have passed bans on smoking on beaches and playgrounds. In San Francisco, Mayor Gavin Newsom said last week that he would go a step further, seeking a 33-cents-a-pack tax to cover the $11 million that the city spends annually to remove cigarette litter.

Nationally, cigarette butts account for one-quarter or more of the items tossed onto streets and other roadways, San Francisco and other cities report.