Then-candidate Muriel E. Bowser delivers remarks during a town hall session for voters last year. A political action committee organized by her allies threatens to factor prominently in next year’s election of council candidates. (Bill O'Leary/The Washington Post)

A majority of the D.C. Council on Tuesday signed on to legislation that would rein in a political action committee run by allies of Mayor Muriel E. Bowser.

Council members said a flood of more than $300,000 in contributions to the group in recent months, mostly by businesses seeking contracts with the city, threatened to corrupt a District government still reeling from an ongoing federal investigation into the last mayoral administration.

“Just what are we becoming here, Tammany Hall?” asked D.C. Council member Mary M. Cheh (D-Ward 3), who introduced the measure with David A. Grosso (I-At Large).

The legislation would close a loophole in city election law that allows a PAC to accept contributions of unlimited size during years in which the group is not actively working to elect a candidate. Ben Soto, treasurer of the pro-Bowser PAC and the mayor’s former campaign treasurer, told The Washington Post last week that he was beginning a fundraising drive to fill the PAC’s bank account with $1 million by the end of the year.

The money is already rolling in through contributions of up to 10 times the legal limit for a mayoral campaign. It would be used by the PAC next year to help reelect allies or unseat council members who do not see eye-to-eye with Bowser, Soto said.

D.C. Council member David Grosso (I-At Large) is the only lawmaker facing re-election next year to publicly opposed the pro-Bowser PAC. (Astrid Riecken/For The Washington Post)

On Tuesday, he pushed back against Cheh’s description of the PAC as anything like Tammany Hall, the notorious political machine that operated in New York City during the 19th and 20th centuries.

“I have a hard time with that when we are completely in compliance with the campaign finance regulations that she signed off on,” he said. “We consider ourselves smart and innovative and doing everything we can to support the mayor.”

Grosso was the only council member up for reelection next year who publicly supported the bill. The other six members who signed on as co-sponsors do not face reelection until 2018.

But Grosso occupies one of the council’s citywide seats that is reserved for non-Democrats, giving him some insulation from PAC spending in the heavily Democratic city. Grosso said he is still concerned that the mayor’s allies could use the money to fund a challenger but said he could not let the unlimited contributions continue.

“Unlimited donations undermine the voice for the people,” Grosso said. Limits “keep elected officials accountable to every individual and not just big donors.”

Whether his legislation could actually stop the pro-Bowser PAC remains unclear.

With only a narrow majority of the council in support, Grosso acknowledged that he and his allies could not pass emergency legislation to halt the fundraising drive of Bowser allies before the end of the year.

And if the council does pass the legislation, it is not clear its backers could override a mayoral veto.

Even if the restrictions were to become law, it is also far from certain that they would survive legal challenges in the wake of U.S. Supreme Court decisions that have protected the right of corporations to make unlimited political contributions.

The legislation could also draw a wide range of opponents, ensnaring District political parties, labor unions and dozens of others who operate PACs to further their members’ causes, lawmakers and experts in election law said.

But Cheh said the damage from the pro-Bowser PAC necessitated council action.

The PAC, which supporters dubbed FreshPAC after Bowser’s campaign slogan of a “fresh start,” “is basically a kind of shakedown of those who are doing business or who want to do business in the District of Columbia,” said Cheh, a professor of constitutional law.

Cheh said the PAC risked tipping the city’s balance of power by intimidating council members to rubber stamp the mayor’s requests.

“The mayor’s supporters unabashedly say, unabashedly admit that they are going to use this tainted money to try to control the votes of the council,” she said.

Council Chairman Phil Mendelson (D) and council member Anita Bonds (At Large), head of the D.C. Democratic Party, signed on in support of the legislation. Three of five new council members elected last year also publicly backed the measure: Brianne K. Nadeau (D-Ward 1), Elissa Silverman (I-At Large) and Charles Allen (D-Ward 6). Silverman and Allen shunned corporate contributions during their campaigns.

Council members Vincent B. Orange (D-At Large), Yvette M. Alexander (D-Ward 7) and Jack Evans (D-Ward 2) did not support the measure. All face reelection next year.

Council members Brandon T. Todd (D-Ward 4), Bowser’s former campaign finance director, and LaRuby May (D-Ward 8), a Bowser campaign organizer east of the Anacostia River, also did not publicly support the measure. They, too, face election next year for full, four-year terms.

Bowser was returning from a conference in London on Tuesday and was unavailable for comment. In a statement, Bowser spokesman Michael Czin said: “We have not reviewed the legislation that would change the rules for PACs — and presumably state parties — for the first time in years. However, we have and will always abide by the rules.”

The legislation now goes before Judiciary Committee Chairman Kenyan R. McDuffie (D-Ward 5). McDuffie helped craft a rewrite of the city’s campaign finance regulations two years ago and left the long-standing allowance for unlimited fundraising in place for non-election years. The limit in election years is $5,000.

City attorneys at the time said they were concerned that eliminating the provision could draw court challenges.

McDuffie promised Grosso and Cheh that he would take up the legislation, the supporters said. But in a statement, he tried to strike a balance between the issues.

“While I recognize the potential for abuse of PACs, any further restrictions to PAC contributions must not run afoul of the decision in Citizens United and its progeny,” he said, referring to the 2010 Supreme Court case.

Health-care companies, developers, and a core group of supporters of Bowser and her mentor, former Mayor Adrian M. Fenty, have pumped more than $300,000 into the PAC since it was launched in April, according to disclosures made last week.

Three Bowser appointees to powerful boards and commissions have contributed $10,000 apiece. A fourth has given $2,500, and a fifth is the PAC’s attorney.

Soto said the PAC would follow whatever the law states. If the council enacts restrictions and the courts uphold it, “we’ll abide by that,” he said. “We want to bring prosperity to all eight wards of the city — that’s our goal.”