Exchanges like this are increasingly common around the world, as communities wrestle with questions about regulating shopping bags distributed at checkout counters. Already countries including China and Ireland and cities including Mexico City have adopted bans or taxes in some form on plastic bags. On Tuesday, officials in San Francisco voted to expand a ban already in place on plastic bags and to require shoppers to pay 10 cents each for paper bags.

The issue has caught the attention of the European Commission, which is expected to issue a preliminary paper on plastic waste this spring. A survey by the commission, published in November, found that about 78 percent of more than 15,000 respondents backed efforts at the level of the European Union to cut the use of plastic bags, and most supported banning them. Janez Potocnik, a Slovenian who serves as European commissioner for the environment, has voiced concerns about “plastic soup” in the oceans — the accumulation of enormous volumes of tiny plastic nodules.

Nonetheless, “it’s unclear whether there will be a proposal on plastic bags” in the forthcoming commission paper, according to Monica Westerén, a commission spokeswoman. If there is a proposal on plastic bags, she added, it will involve pricing measures like a fee for bags and a target for reducing them, rather than an outright ban.

A number of European countries already have bag taxes in some form, or other policies aimed at reducing the use of plastic bags. But there is substantial variation among countries and even types of stores. That can be confusing to travelers.

“We shouldn’t hang around and wait for national legislation to be imposed one state at a time, because it could take years before each country puts in place the right sort of disincentives,” argued Chris Carroll, a representative of Seas at Risk, an environmental group based in Brussels that is seeking action at the E.U. level. The average European still uses as many as 500 plastic bags each year, he said, many of them only once.