Matt Mahan’s floundering campaign for California governor was hit with a bombshell complaint accusing the San Jose mayor of illegally coordinating with a billionaire-funded PAC.

The Post exclusively obtained the complaint, which accused Mahan and an independent expenditure committee called Back to Basics of violating state election law on coordination by using same polling company, Impact Research, and each paying the firm $89,500.

Allegations made to the state’s Fair Political Practices Commission noted that similar sharing of “key strategists” has resulted in major fines in the past.

However, in a curious twist, the FPPC’s website on Friday afternoon showed the complaint had been rejected and the case was closed despite officials for Mahan’s campaign and the pro-Mahan committee being unaware that a complaint had been filed last week.

Officials for the FPPC did not respond to a request for comment on why and when the case was closed.

Tasha Dean, a spokesperson for the Mahan campaign, called the complaint a “desperate, politically motivated attempt to manufacture a story.”

“It’s unfortunate for the sake of our democracy that detractors will stoop so low as to make patently false complaints,” she said.

Political experts told The Post that Mahan’s use of the same polling firm as the pro-Mahan committee was unprecedented, “sloppy” and “unseemly.”

Mahan, who is polling in sixth place, has been in a free-fall this week, as billionaire donors like Netflix co-founder Reed Hastings — who clawed back $1 million from the pro-Mahan committee — are jumping ship.

Other billionaire backers to the pro-Mahan committee have included venture capitalist Michael Moritz, Los Angeles businessman Rick Caruso and Stripe CEO Patrick Collision.

The Back to Basics committee has already raised and spent more than $23 million supporting Mahan’s gubernatorial campaign, which has reportedly led to him missing more than third of San Jose city council meetings since he launched his campaign in January.

The complaint accused the IE committee of using of “shared key strategists” on polling, and campaign finance filings cited in the complaint show the PAC paid Impact Research $89,500 in February 2026 for polling and strategic consulting services. Mahan’s campaign later paid the same firm another $89,500 in April.

Impact Research has previously done polling for Presidents Barack Obama and Joe Biden, as well as Hillary Clinton’s campaign for president.

The complaint marked the second time Mahan and the Back to Basics committee have been accused of illegal coordination in a formal complaint to the state’s Fair Political Practices Commission.

David Latterman, a longtime political analyst in San Francisco who spent nearly two decades working on campaign polling operations, called the more recent allegations “unseemly” and unprecedented.

“They’ve put themselves in a position where it looks like collusion,” Latterman said. “You still have to prove it, but I can’t even think of a time where I’ve heard of this happening before.”

Candidate committees are bound by more restrictions than independent committees that can raise unlimited sums of money. Among the PAC’s biggest donors was Moritz, the influential former Sequoia Capital chairman, who contributed roughly $3 million combined. 

Caruso kicked in at least $1.25 million through direct and affiliated donations, while Reddit CEO Steve Huffman gave nearly $1 million, and Collison contributed roughly $1.49 million across multiple donations.

Michael Trujillo, a political consultant who who works for a pro-Antonio Villaraigosa campaign committee and filed the previous FPPC complaint against Mahan over allegedly illegal coordination with the Back to Basics, called the polling arrangement “more than just sloppy — it’s plain dumb and stupid.”

“It goes to the arrogance of Silicon Valley thinking they don’t have to play by the rules and break everything,” Trujillo said.