The Washington, D.C., bag tax seemed simple enough: Beginning Jan. 1, grocery stores in the district would charge five cents a bag, plastic or paper. The goal was to cut down on waste and raise money to clean up the polluted Anacostia River.

But nearly a month into the program, it’s turning out that government is having trouble legislating its way out of a plastic bag.

The levy got off to a relatively smooth start in the district’s grocery stores, some of which handed out free reusable bags to ease the pain. Then things got complicated.

To help the environment in Washington, D.C., a new tax has been placed on plastic and paper bags. But as Neil Hickey reports, the law’s complexity is giving some businesses a headache.

The law, passed unanimously by the City Council and signed into law in July, applies to anything sold at any store that sells food. But deciding what constitutes a food store is easier said than done.

Politics & Prose, a well-known local bookstore, sold one food item-mints-including a variety that came in a tin with Barack Obama’s likeness. To be safe, and avoid charging every customer who bought a book five cents a bag, the store dropped the mints. “It’s all been a little bit unclear,” says Tracey Filar Atwood, general manager. “Those items are not really at the core of our business. It was a very easy decision to make not to stock them,” she says.

The owners of Chocolate Moose, which sells quirky gifts and jewelry as well as candy, were certain the tax didn’t apply to them. Although they received the notice the district sent to all retail food establishments, candy accounts for just 10% or 20% of sales, says co-owner Marcia Levi. “I don’t consider myself a food establishment,” she says. When another store owner asked what she was going to do about the regulation, she decided to call the city, just to be on the safe side. “I explained to them the situation-that only a small part of my business is food,” she said. “They said it does not matter.”

So Chocolate Moose now charges a nickel a bag.

Pleasure Place, an adult toy store, so far isn’t charging for bags-even though it has a license to sell food, including edible body frosting. “I’m not sure if it applies to me,” says Cecilia Colglazier, the owner. Victoria’s Secret, which sells mints, edible body icing and edible shimmer powder, along with its trademark negligees, isn’t charging for bags either-at least not yet.

The District of Columbia is the only major U.S. city to tax both paper and plastic bags. In San Francisco, disposable plastic bags are banned in large supermarkets and pharmacy chains, but paper bags are OK if they are made from recyclable materials and can be recycled. In North Carolina, plastic bags are banned in some Outer Banks counties but retailers can provide recycled paper bags.

Tommy Wells, the Democratic councilman who introduced the D.C. bag-tax bill, says it was written deliberately to apply to all retailers who sell food. After studying other cities where bag bills were defeated, Mr. Wells discovered that “it generally started with the grocery stores who helped defeat those bills,” he said. Local grocery stores asked the council to avoid putting them at a disadvantage with other retailers. “For example, Target sells food. It needs to cover Target as well, or it’s an unfair impact,” he said. So now the Target store in D.C. charges five cents a bag, too.

The City Council did make clear that the five-cent tax doesn’t cover all bags. But keeping track of the bags that are excluded can be a daunting task.

The law specifically excludes bags that “package bulk items, such as fruit, vegetables, nuts, grains, candy, or small hardware items.” It also excludes those that “contain or wrap frozen foods, meat, or fish…flowers, potted plants, or other items where dampness may be a problem.” Other exceptions include unwrapped prepared foods and bakery goods, as well as bags provided by pharmacists to contain prescription drugs, newspaper bags, door-hanger bags and laundry dry-cleaning bags. Also tax free: “Bags sold in packages containing multiple bags intended for use as garbage, pet waste, or yard waste bags.”

By law, a restaurant patron who requests a doggie bag doesn’t have to pay a nickel-as long as the bag is paper, not plastic. “When you go to a nice restaurant and you want a doggie bag, you may have already cleared the bill,” Mr. Wells said. “You don’t want to go through this whole nickel kind of relationship.”

A takeout sandwich shop, however, has to charge unless it has chairs and tables, in which case it doesn’t have to charge as long as the bags are paper, 100% recyclable, made of at least 40% post-consumer recycled content and say something like “Please Recycle This Bag” in highly visible type on the outside of the bag. Banned altogether at food and drink establishments: plastic bags that can’t be recycled (the opaque plastic kind).

Stores keep one cent of every five cents they charge for bags, and two cents if they give customers a credit of at least five cents for each bag (of any sort) that they bring to the store. That provision forced clerks at one local Giant supermarket to intervene in every purchase at every self-check-out terminal to authorize the credit. Under no circumstances, the law says, are stores allowed to pick up the five-cent fee for their customers.

The minutiae of the law seems to frustrate business owners more than residents, who, three weeks into the new rule, are resigned to toting around backpacks, bright green recyclable Giant Food bags or paying the levy. But some still aren’t used to it. “It’s very aggravating,” said Rosa McNair, 80 years old, as she walked out of Target with a five-cent plastic bag. “What are you going to do, carry all your boxes on the bus?”

A spokeswoman for the district’s Department of the Environment, which helps enforce the law, said regulations are due out this week that will clarify the situation. The district is projecting $3.5 million in revenue from the bag tax this year, with the total declining steadily over the next four years.

Administrative costs for the first year, including a compliance officer, are projected to reach $105,450. The law carries a fine of $100 for the first violation after a warning. No one has been cited, yet.

This article was written by Sara Murray for the Wall Street Journal.