In the city's toughest neighborhoods, narcotics officers routinely bust mini-marts and bodegas for selling tiny ziplock plastic bags.
Police consider the bags to be drug paraphernalia. But many store owners say they bought the bags legally from tobacco wholesalers and other distributors and thought they could sell them.
At issue is whether the buyer is using the bags for drugs or for legitimate items like coins, jewelry, stamps and small amounts of tobacco.
"The question is whether the item is for a legal function or an illegal function," said Tennessee-based lawyer Robert T. Vaughn, an expert on drug-paraphernalia laws.
Under Pennsylvania law, selling the bags is a crime if the shop owner "knows or should reasonably know" that the buyer intends to use them for drugs.
To make their case, police officers often use informants to ask store owners for "weed bags" or "rock bags" - street lingo for marijuana and crack.
The Daily News interviewed seven shop owners who were arrested in either 2007 or 2008 for selling the bags. Most struggle with English and say they didn't understand the charges and needed interpreters in court.
"I kept saying, 'We don't understand the problem,' " said Korean-born David Nam, whose Olney smoke shop was raided in 2007.
In some cases, police found a large number of ziplock bags - "hundreds of thousands" in one store alone, according to a court document - and some shop owners said they suspected that some were used for drug packaging.
But others said they had no clue. And all contended they didn't realize it was illegal.
Emilio Vargas, who owns the building housing the Dominguez Grocery Store, on Potter Street in Kensington, which was raided in March 2007, said he never would have sold the bags if he had known.
"If you say they're illegal, I won't sell it," Vargas said. "If you say it's illegal to sell Pepto-Bismol, I don't sell it."
But cops and prosecutors say they don't believe store owners are that naive.
"They know who's buying and what it's for," said Jerry Rocks, a detective in the District Attorney's Office who also founded a neighborhood group to fight the sale of drug paraphernalia.