Cigarette butts, the most littered items in the world, are posing an intractable trash problem for regulators and tobacco companies: Throwing them on the ground is a firmly entrenched habit for many smokers.

Regulators are taking a tougher stance on cigarette filter pollution amid concerns about the environmental impact of single-use plastic. Butts for decades have been made from cellulose acetate, a form of plastic, which takes years to break down. Studies show that butts—which often wash from sidewalks into drains and then...