The last time there was an open mayoral election in New York City, an independent committee spent roughly $900,000 to help take down the presumptive front-runner, paving the way for Bill de Blasio’s victory.

Eight years later, another onslaught of barely regulated money is heading New York’s way, with super PACs poised to play an outsize role in the race for mayor the most important election in recent city history.

Business-friendly organizations have already raised millions of dollars. At least one candidate, Raymond J. McGuire, has a dedicated super PAC. And now progressive groups are getting in on the act, creating their own super PACs to supplement their on-the-ground and social media efforts.

The rising tide of independent spending highlights the fierce debates unfolding across the political spectrum about how to manage the city’s post-pandemic recovery and what its future should look like.

It also points to a hunger among donors in New York City — one of the nation’s political fund-raising capitals — to play a role in this year’s races without being bound by the strict rules governing direct donations to political campaigns.

A super PAC called New York for Ray, which backs Mr. McGuire, a former Wall Street executive, has already raised more than $1 million since registering with the state in January, including $500,000 from a theater producer, Daryl Roth, whose husband, Steven Roth, is the head of Vornado Realty Trust; and $500,000 from John Hess, the chief executive of Hess Corporation. It also lists a $2,500 donation from Richard S. Fuld Jr., the former chief executive of Lehman Brothers.

At the other end of the spectrum, a group of progressives are starting a super PAC that aims to raise up to $5 million, in hopes of pushing the field of more than 30 mayoral candidates and hundreds of City Council candidates to the left on matters including housing and diverting funding from the police.

The super PAC, Our City, is being led by Gabe Tobias, a former senior adviser to Justice Democrats, which played a key role in helping Representative Alexandria Ocasio-Cortez get elected to Congress. Mr. Tobias is also the co-founder of the Movement School, which grew from her campaign.

Our City’s board includes Nelini Stamp, a senior official at the Working Families Party, and Ed Ott, the former executive director of the New York City Central Labor Council.

“There’s no other effort like this in recent history that I’m aware of, a progressive independent expenditure aimed at winning control of city government,” Mr. Tobias, the director of the group, said. He is hoping to raise $300,000 in the group’s first month and go from there.

Several of the leading candidates running in the June 22 Democratic primary for mayor are battling to emerge as the progressive standard-bearer, continuing a trend that has influenced a slew of recent elections from House races to City Hall.

But various business interests in New York are trying to mount a counterattack: They persuaded Mr. McGuire, one of the highest-ranking and longest-serving Black executives on Wall Street, to enter the race; they have urged their employees to register to vote in the primary; and they are raising money to push their issues.

James L. Dolan, the chief executive at Madison Square Garden Entertainment, has already started The Coalition to Restore New York, a super PAC to which he has directed more than $2 million in monetary and in-kind donations from the various Madison Square Garden affiliates he controls.

Mr. Dolan declined an interview request, but his PAC says it is focused on getting the candidates to explain how they would restore the city’s economy, improve public safety and balance its budget.

Stephen M. Ross, the developer of Hudson Yards, has put $1 million toward a super PAC called Common Sense NYC, which has a similar political bent as Mr. Dolan’s. It was originally considering targeting both the mayor’s race and the City Council races, but the crowded mayoral field inspired it to focus on the City Council, where it can presumably make more of an impact.

The group recently spent roughly $200,000 on a special election for a Council seat in Queens, helping a former councilman, Jim Gennaro, defeat several rivals including Moumita Ahmed, a progressive whose views the group called “extreme” and “reckless.”

“It completely changed the race in the final two weeks,” Ms. Ahmed said. It also turned Mr. Ross, who has supported both former President Donald J. Trump and Senator Chuck Schumer, the majority leader, into even more of a boogeyman for the left. (Mr. Ross, whose company owns a controlling stake in Equinox, ignited anger among Democrats in 2019 when he hosted a fund-raiser for Mr. Trump.)

Our City’s launch video juxtaposes a picture of Mr. Ross at Hudson Yards with an apparently homeless person sleeping on a cardboard box as a narrator talks about inequality. Mr. Ross declined to comment on the video.

The New York Immigration Coalition is also planning to mount an independent expenditure committee, according to Murad Awawdeh, the group’s interim co-executive director.

“What progressive organizations and progressives have realized is that super PACs are going to be part of the narrative, and until we have real reform that outlaws them, we have to be able to play the game and participate in that process,” Mr. Awawdeh said.

In New York City, candidates running for mayor, and donors seeking to support them, are subject to strict limitations: Individuals who are doing business with the city can contribute up to $400 to a mayoral candidate; other donors are subject to caps varying between $2,000 and $5,100. Wealthy individuals and corporations can make unlimited contributions to a super PAC under New York and under federal law, according to Seth Agata, a former counsel in the governor’s office who helped write New York’s independent expenditure regulations.

Even as more super PACs are expected to form in the weeks ahead, it remains to be seen whether outside spending eclipses the nearly $16 million spent during the 2013 New York City elections.

Veterans of the mayoral primary that year recall only one independent expenditure committee that mattered. The committee, New York City Is Not for Sale, received backing from an animal rights group seeking to ban horse-drawn carriages. It focused on the race’s putative front-runner, Christine Quinn, then the City Council speaker.

The effort ended up mired in controversy. But Ms. Quinn said it had a clear impact on her mayoral prospects.

“These independent expenditures are merely ways around the best campaign finance law in the country, and I think they’re very destructive,” she said.

New York for Ray is supposed to have a more positive message. Its goal is to increase Mr. McGuire’s name recognition and amplify his message, according to someone involved in the effort.

“I have known Ray McGuire a long time and am confident in his ability to lead our city,” Ms. Roth, one of the group’s major donors, said. Mr. Hess, via a spokeswoman, declined to comment.

It will be led by Quentin Fulks, an Illinois-based political consultant; Jennifer Bayer Michaels, a former fund-raiser for Gov. Andrew M. Cuomo; and Kimberly Peeler-Allen, an experienced New York fund-raiser who is also the co-founder of Higher Heights for America, an organization that aims to elevate Black women in politics, and the co-chair of its PAC.

L. Joy Williams, who is working on Mr. McGuire’s campaign, is the Higher Heights PAC’s chairwoman. A campaign spokeswoman said Ms. Williams was unaware that Ms. Peeler-Allen was working on New York for Ray, and that there has been no coordination between the super PAC and the campaign.

A serious super PAC effort on Mr. McGuire’s behalf — especially through paid advertising — could help him overcome his significant challenges with name identification. Among New York political operatives, the matter of whether Mr. McGuire would receive outside help had been a subject of great speculation. In recent months, there have been conversations within prominent Democratic firms about the prospect of doing work for a pro-McGuire independent expenditure effort, according to someone familiar with the conversations.

The super PAC sees no gain in smearing Mr. McGuire’s opponents, the person involved in the effort said, given the advent of ranked-choice voting, which will allow New Yorkers voting for mayor to rank their top five choices.

“Rule No. 1 is do no harm,” said Jesse Ferguson, a Democratic strategist who has worked on multiple national independent expenditure efforts and lives in New York. “That means understanding how what you say in the campaign could reverberate on your preferred candidate, and how your entrance into the race could even reverberate on your candidate.”