The sponsor of a proposed plastic bag ban in Suffolk withdrew that idea Thursday and instead introduced a bill to impose a five-cent fee on plastic and paper bags given away at store checkouts.

Legis. William Spencer (D-Centerport) said he was unsure whether he had the votes to pass the outright ban on the thin plastic bags and was persuaded by opposition from the union representing grocery store workers.

Spencer was confident he had the votes to pass the five-cent fee, which would go into effect in 2018. The nickel-per-bag fee would be kept by the grocery and convenience stores and be similar to legislation that recently passed the New York City Council.

The fee “has been very effective around the world in reducing plastic bag usage,” Spencer said.

Environmentalists had pushed the outright ban as the best way to eliminate plastic bags, which end up as litter on roadways and pollute waterways, and are made from fossil fuels. But grocery store owners and plastic bag manufacturers had argued it would burden consumers and hurt the stores.

Spencer said such fees have reduced plastic bag usage by up to 85 percent in places such as Washington, D.C., though a Washington Post article last year said that widely reported estimate has since been discredited and estimates vary.

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Adrienne Esposito, executive director of the Citizens Campaign for the Environment, who had been the most vocal advocate of the ban, declined to comment on the new version of the bill.

Kevin McCallister, executive director of nonprofit Defend H2O, said, “A 5 cent fee isn’t going to be a deterrent for using store-provided bags. There must be an outright ban, otherwise plastics will persist.”

Grocery store owners and plastic bag manufacturers urged lawmakers last month to switch from a ban to a fee. Store owners said they already were facing an eventual increase in the employee minimum wage to $15 an hour.

Spencer said he had been contacted by Local 338 of the Retail, Wholesale, Department Store Union/United Food and Commercial Workers, which said it was worried about a bag ban’s effect on stores and how it could affect negotiations on new contracts.

A public hearing on the new bill is scheduled for July and a final vote in August.