The ban intended to cut down on pollution requires grocers and other retailers to stop handing out plastic bags and charge customers a nickel fee for every paper bag as a way encourage people to bring their own bags.
Stores have posted signs telling customers of the upcoming changes. The city has mailed out thousands of notices to local retailers, as well as calling and visiting them in-person. One group at the University of Washington even held an exchange to encourage people to bring their extra reusable bags, or come get one.
"I think the stores will be ready, I don't know if the customers are ready. It's just a matter of getting used to something new," said Joe Gilliam, president of the Northwest Grocery Association, which represents the largest grocery chains in Seattle.
Customers who are unaware will show up wondering why they can't get a plastic bag, he said. "There will be an adjustment."
Local retailers have been "training employees and trying to educate their customers in advance so there's not a backlash at the counter on implementation day," said Jan Gee, spokeswoman for the Washington Food Industry Association, which represents more than two dozen independent supermarkets in Seattle.
"Our industry has been preparing for it for a long time," she said.
Plastic bags have been blamed for littering streets, fouling oceans and harming marine life. Each year Seattleites carry off about 292 million single-use plastic bags, and 68 million paper bags. About 82 percent of paper bags are recycled, while only 13 percent are recycled.
The city council unanimously approved the plastic bag ban last December, joining other cities across the country. Nearby communities such as Bainbridge Island, Mukilteo, Edmonds, Bellingham and Portland, Ore., also have banned plastic bags.
In 2008, the Seattle City Council voted to charge a 20-cent fee on paper and plastic bags, only to have the measure overturned by voters in a referendum bankrolled by the plastics industry the following year.
The plastic-bag industry has denounced the upcoming ban.
"Seattle's plastic bag ban will have an immediate negative impact on the wallets of Seattle shoppers and, ironically, the environment," Mark Daniels, head of the American Progressive Bag Alliance, a group representing plastic bag manufacturers, said in a statement last week.
Daniels said his group would seek "a comprehensive statewide recycling solution that address all forms of plastic bags, sacks and wraps."
Thin plastic bags - less than 2.25 millimeter - are banned from grocery, department and other retail stories, although merchants will be allowed to use up their inventory. Bags used to package bulk items, produce or meat will still be allowed. Customers using vouchers or electronic benefit cards from food-assistance programs are exempt from 5-cent fee. Retailers would keep the nickel to help defray costs of paper bags. Plastic bags from restaurant orders are allowed.
"Hopefully things will smooth out after a week or so and customers will not be too mean to our cashiers," she said, laughing. "The city did it and not us."