In a season rank with the stench of money in politics, you’d think that a piece of legislation that would strike a small blow for better government, a wiser use of public funds, would sail through the New York City Council.

You might think that, but you would be wrong.

Right now, the speaker of the Council is sitting on a bill that would make sure that public money available under the city’s imperfect — but pretty good — campaign finance law would not be used to bulk up the power of lobbyists.

The speaker, Melissa Mark-Viverito, a Democrat, would not explain her thinking, when she might make a decision or whether she was speaking with lobbyists whose financial clout the new law would curb.

In theory, under a law passed several years ago, people doing business with the city are limited to giving at most $400 per candidate. Look closely, though, and you can see the wormhole that hundreds of thousands of dollars flows through. Here’s how it works.

The city rewards campaigns that receive many small contributions, allotting $6 in public money for every $1 donated, up to a total of $175. A person can give as much as $4,950, but only the first $175 is matched. The law has the virtue of making a relatively modest donation of $175 worth $1,225 to the candidate. It is a democratizing force.

Moreover, for people doing business with the city, nothing they give is matched with public dollars.

But there’s a side door. It is called bundling. When a lobbyist gathers donations from many people, the money is heaped together in a pile — the bundle — and while no individual donation can exceed the maximum, the lobbyist has done a major favor for the candidate. For instance, in the 2013 elections for the city’s top two elected offices, mayor and comptroller, nearly $1 million came in through 10 bundlers, most of them doing business with the city. In the mayor’s race, the top five gave about $600,000 to the campaign of Bill de Blasio, a Democrat; the five leading bundlers in the Scott M. Stringer’s Democratic campaign for comptroller brought in $447,000. Altogether, bundlers gave $2.7 million to campaigns in the city.

The democratizing power of public financing is twisted in this process.

Even though contributions from the bundlers themselves were not, in general, eligible to be matched with public money if they were doing business with the city, the individual contributions within their bundles did qualify. During the 2013 election, the public provided approximately $1.2 million additional money to what the bundlers brought in.

Photo Ben Kallos, a Democratic councilman who is the chairman of the committee on governmental operations. Credit Ángel Franco/The New York Times

In effect, the public was paying to give the bundlers even more clout.

“The city should not be providing public dollars to amplify the already strong voices of special interests,” said Ben Kallos, a Democratic councilman who is the chairman of the committee on governmental operations. In May, he held a hearing on a bill that would eliminate the matching contributions for money bundled by someone doing city business. Mr. de Blasio’s counsel, Henry Berger, testified in favor.

“Lobbyists play a number of roles in city government, some of which are very, very important,” Mr. Berger said. “Their influence on the electoral process as demonstrated in the 2013 campaign is significant, and can be reduced by this, and we think it is appropriate to do so.”

Gene Russianoff, a lawyer with the New York Public Interest Research Group, long an advocate for the public financing of campaigns, testified that the Council had first considered the loophole a decade ago but did nothing.

“They made a mistake in 2006,” Mr. Russianoff said. The bundlers had every right to solicit money for campaigns, he said, but they should not be given public funds. “We have nothing against them expressing their views, but, you know, take your hands out of my pocket,” he said.

The money involved is only a tiny fraction of city spending, but Dick Dadey, executive director of Citizens Union, said, “It’s really the principle behind it.”

Mr. Russianoff said the Council could take a stand by passing the bill. “It has been a time of people’s cynicism and despair in government,” he said. “The only ones who would benefit from this law not passing are those special interests.”

Suri Kasirer, a leading city lobbyist, said she was in favor of the bill; leaders of two other major lobbying firms, John Del Giorno and James Capalino, did not respond to requests for comment.

Asked three times by email whether Ms. Mark-Viverito was speaking with lobbyists about the bill, her spokesman, Eric Koch, replied: “Speaker is reviewing the bill and it’s going through our normal legislative process.”

Email: dwyer@nytimes.com