Profit margins for grocery stores are so narrow that a key to gaining the support of supermarket chains is to make sure the legislation doesn't increase their costs, Wells said.

Plastic bags cost about 2 cents apiece for stores to provide, Wells said. Paper bags cost 5 cents.

Both the Washington law and the Baltimore proposal allow merchants to keep a portion of the money collected for administrative costs.

Some supporters of the city legislation want to see the money the bag fee would raise be used to enhance Baltimore's green efforts. Kraft has also introduced pending legislation that would create a special fund for park restoration and sustainability projects.

Jamie Miller, a spokesman for Giant, said the supermarket chain hasn't taken a position on the current proposal.

"We're still reviewing it to determine what impact it would have on a customers and business," Miller said. He added that Giant stores in the Washington area have done well implementing the fees.

Lee Califf, director of the American Progressive Bag Alliance, a plastics industry group that opposes campaigns targeting plastic bags, said the bill in Baltimore is bad policy.

"In this tough economy where food prices continue to rise, the government should not be adding what is essentially a regressive tax," Califf said in a statement. "The proposed bag tax will be a burden on already overtaxed, hardworking Baltimore families and businesses, and risk putting hundreds in Maryland who rely on the industry for employment out of work."

Califf said the city should look toward a robust recycling program instead.

"If lawmakers are interested in protecting the environment, they should consider the facts and not force 'feel good' legislation that does more harm than good," he said.

While many customers say they wouldn't mind paying an extra five cents for disposable bags, Phoenix Yu of Owings Mills said she'd just quit shopping in Baltimore.

"That's a bad idea," said Yu, who stopped at the Giant on 41st Street in North Baltimore on a recent day to pick up a few items. Customers can't control the number of plastic sacks the cashier or bagger uses to pack their groceries unless customers do it themselves, Yu said.

Betty Reynolds of the city's Medfield neighborhood said she makes a habit of bringing reusable bags to the grocery store, and she wishes more people would do the same. "And we won't have these things floating all over the place," she said, pointing to the plastic bags that held her groceries on a day she forgot her own sacks.

Lawson, of the Trash Free Maryland Alliance, said environmentalists are working to recruit supporters of the legislation by building on cleanup efforts being done in Baltimore, including weekly recycling pickup, trash bins on sidewalks, newly expanded street sweeping and a pilot program to provide huge plastic trash cans on wheels with attached lids.

"Plastic is chemically designed to last for centuries, and its intended use is only for a few minutes, even if you reuse them," Lawson said. "Very few end up being recycled."

What's more, Lawson said, the public is already paying a cost for the bags, which is embedded in the price of groceries and in tax dollars dedicated toward litter reduction and environmental cleanup.

"Once that cost is made more transparent to people, they realize it's time to make a different choice," she said.

Baltimore Sun reporter Luke Broadwater contributed to this article.