He failed to qualify for matching state campaign funds and fell short of the threshold to participate in two upcoming debates as he runs for governor of New Jersey. His spokesman works for a consulting firm in Washington, D.C., and he has no paid campaign manager.

But Sean Spiller has something the other five Democrats running for governor don’t: a $35 million blank check from a group with close ties to the labor union he leads, the New Jersey Education Association.

For more than six months, Mr. Spiller’s image has been plastered on billboards, campaign mailers and front-door hangers throughout New Jersey. He has been featured in commercials, digital posts and, more than a year before November’s election, a full-page ad in The New York Times.

The publicity has been paid for by Working New Jersey, a super PAC funded largely with public schoolteachers’ union dues, according to a review of Internal Revenue Service records.

Since July, I.R.S. records show that a political arm of the teachers’ union has sent at least $17.25 million to Working New Jersey. The super PAC, in turn, has reported that it was prepared to spend as much as $35 million on behalf of Mr. Spiller, a science teacher by trade who draws a roughly $370,000 salary as president of the N.J.E.A.

Working New Jersey has already spent $8.3 million on television, digital and streaming ads, according to AdImpact, which tracks political spending.

The union’s unconventional strategy appears to have helped boost Mr. Spiller’s standing in the hypercompetitive race.

Early surveys indicated that Mr. Spiller, a little-known former mayor of Montclair, N.J., had limited political support. But recent polls have suggested that he is now tied for second place. Representative Mikie Sherrill has consistently been at the front of the pack, with Mr. Spiller and the mayor of Newark, Ras J. Baraka, and the mayor of Jersey City, Steve Fulop, close behind her.

But nothing about the race to replace the state’s term-limited governor, Philip D. Murphy, is certain with such a large and accomplished field of candidates. Fundamental changes to the rules that govern primaries have made it the state’s most volatile contest in recent history.

A poll conducted in January by Emerson College found that 56 percent of Democrats remain undecided.

The N.J.E.A. has long been among the state’s most powerful unions, with nearly 200,000 members and a willingness to take on political foes. Its involvement with the Working New Jersey PAC is among its most overt efforts to sway voters in a state election.

Mr. Spiller, who emigrated from Jamaica as a child, has said that as governor he would focus on expanding affordable housing, strengthening schools and defending New Jersey against President Trump’s policies.

Most of the Democratic and Republican candidates for governor are benefiting from spending by outside interest groups. But Mr. Spiller is the only candidate to have also raised so little on his own to directly fund his campaign. As of the most recent state filing, Mr. Spiller’s campaign had raised $183,000 in a race where every other prominent candidate collected more than $1 million — and several have taken in close to $3 million each.

In an interview, Mr. Spiller, 49, said there were metrics beyond fund-raising and the size of a campaign staff that were more indicative of support for his candidacy. He noted that he had submitted more signatures to get on the ballot than all but one other Democratic candidate.

He refused to directly address questions about whether he considered it a conflict of interest that he was benefiting so significantly from dues contributed by members of a union that employs him as president. He noted that other candidates had turned to real estate developers and Wall Street bankers for contributions, and that by sidestepping that funding stream he had avoided being beholden to their interests, if elected.

“Our campaign is based on fighting for working class folks,” he said.

He also dismissed the significance of falling short of the $580,000 campaign fund-raising threshold that would have qualified him for 2-to-1 matching funds for the June 10 primary. “If I called millionaires and very wealthy folks, I could meet goals,” he said.

By law, super PACs may raise and spend unlimited sums but are barred from explicitly coordinating with candidates’ campaigns. Officials with the N.J.E.A. and Working New Jersey said that Mr. Spiller had not been involved in allocating union funding or in any promotional efforts on his behalf.

“We recognized the need to put guardrails and protections in place to ensure that there was not a conflict of interest,” said Steven Baker, the union’s spokesman. “The candidate does not get to decide what is spent or how it is spent.”

Mr. Baker said Mr. Spiller also had no role in the union’s decision to set aside money for political advocacy or for its political arm to send millions to Working New Jersey.

A spokesman for Working New Jersey, Eddie Vale, said the same thing. “As an independent expenditure campaign, we cannot, and do not, coordinate with or talk to the Spiller campaign in any way,” Mr. Vale said.

To voters, however, the Spiller promotional material piling up in mailboxes may be largely indistinguishable from the types of ads paid for directly by his opponents’ campaigns. Each carries a tiny disclaimer: “not made with the cooperation or prior consent of, or in consultation with or at the request or suggestion of, any candidate, or any person or committee acting on behalf of any candidate.”

Specialists in campaign finance law say that Working New Jersey’s support for Mr. Spiller is part of a growing trend of outsourcing to special interest groups work traditionally done by campaigns.

Daniel Weiner, an election law expert at New York University’s Brennan Center for Justice, noted that Mr. Trump also relied heavily on super PACs for core campaign responsibilities.

“Every election cycle people push the envelope even further,” Mr. Weiner said.

The trend can be traced to the Supreme Court’s Citizens United campaign finance decision in 2010, which freed political action committees run by corporations and unions to spend unlimited sums on behalf of candidates.

“The theory was that these groups would not be interchangeable with candidates’ campaigns,” Mr. Weiner said. “Instead, the way they often work is they’re just sort of the alter ego of the campaign.”

Only New Jersey and Virginia hold governor’s races the year after a presidential election, and their results are likely to offer some of the nation’s earliest insights into voter attitudes toward Mr. Trump ahead of the 2026 midterm elections.

It is perhaps no surprise that New Jersey’s contest is on track to hit campaign spending levels that one top state elections official called “stratospheric.”

That’s true of super PACs, too.

In 2021, super PACs spent a record $13.4 million in support of all primary candidates for New Jersey governor. That record has already been dwarfed by the $35 million in anticipated spending by a single super PAC on behalf of Mr. Spiller.

In the days leading up to the March 24 deadline to qualify for matching funds, Mr. Spiller’s appeals to potential donors took on an urgent tone.

“I need you to donate $20 or more,” one email stated. “I’ll be honest with you,” another read, “we’re not yet where we need to be.”

But his shortage of funds appears to have had no effect on Working New Jersey’s ability to spread his message.

Officials running the super PAC said that they had conducted 13 internal polls to measure Mr. Spiller’s standing in the race and are prepared to continue targeting Democratic primary voters on television, social media, billboards and at their homes.

Last Friday, people affiliated with Working New Jersey hung fliers on doors in Cranford, N.J. — an effort that the officials said was part of a statewide canvassing blitz that had already reached 661,000 homes. At one house, after leaving a door hanger, the representative sent a text message to the registered Democrat in the household with a link to the super PAC’s website: “New Jersey needs fighters like Sean to stand up to the Trump administration’s radical agenda and do something about rising costs.”

Should he lose, Mr. Spiller is likely to face questions about the wisdom of investing teacher dues so heavily in a single political campaign.

“He’s going to have to face his members” and explain spending millions of dollars, said Matthew Frankel of the Sunlight Policy Center, a nonprofit advocacy group critical of N.J.E.A. leadership.

“On that,” Mr. Frankel added, “I think he’s in a world of hurt.”

Mr. Baker, the union spokesman, said that the N.J.E.A.’s endorsement of Mr. Spiller and financial support for his candidacy were based on a conviction that he could “most forcefully and effectively advance” members’ priorities.

Those priorities, he said, are multifaceted and include improving pension allocations, fully funding schools and defending freedom to read initiatives.

“When you look at the national landscape, voters are very aware of what’s at stake in a state like New Jersey,” Mr. Baker said.