As election day nears, contributions are flooding into the campaigns for and against San Francisco’s November ballot initiatives, with Airbnb putting up more than $8 million to fight tougher restrictions on short-term rentals.

The new campaign finance reports, covering the period from July 1 to Sept. 19, involve not only the city’s 11 ballot measures but also Mayor Ed Lee’s re-election bid, a fight for the District Three supervisor’s seat and a number of other local races.

The biggest money is showing up in the battle over Proposition F, where Airbnb is battling a measure that would tighten the rules for turning homes into impromptu hotels. With plenty of cash also flowing into the other side, the proposition is shaping up to be the most expensive and contentious on the ballot.

Prop. F would cap vacation rentals at 75 nights per year for each home or apartment and impose steep fines on companies like Airbnb or Homeaway for listing rentals that don’t comply with city law. It would require housing platforms and hosts to give the city quarterly reports on how many nights properties had been rented. SF for Everyone, which opposes the measure, has raised more than $3.2 million since July 16, and $4.6 million more on Sept. 24, after the campaign finance deadline passed, for a total of more than $8 million. The campaign — almost entirely funded by Airbnb — has spent $3.6 million.

Largest donors

The proposition is backed by Share Better SF — whose members include landlords, housing activists, unions and neighborhood groups. They have raised $200,117.04 in support of the measure. Since July 1, it has received $89,312.58 in donations.

The San Francisco Apartment Association was one of the biggest donors, contributing more than $20,000. But its biggest donor is Unite Here, a union representing hotel workers, a group threatened by the growing popularity of short-term rentals in the city. The union gave $50,000 during the most recent finance reporting period and another $50,000 on Sept. 23, just days after the reporting deadline, bringing its total contribution to $200,000.

Construction freeze

A similar trend has emerged for Proposition I, which would put a moratorium on the construction of market-rate housing in the Mission District. A campaign in support of it, the Committee to Save the Mission, has raised $79,222.06, with more than half — $47,957.14 — coming in since Aug. 1.

The group against it, San Franciscans for Real Housing Solutions, has collected about $500,000 since July 1. The biggest donors include real estate companies like Wilson Meany, which donated $10,000, and the Toboni Group, which donated $25,000. Another $200,000 was donated on Sept. 23 by the California Association of Realtors, based in Sacramento, bringing their total contribution to $237,000.

Fundraising for Lee’s re-election campaign has slowed in the past few months, although with no strong challenger in the race, that’s not really a concern. He has raised $1.18 million — just $76,000 since the last finance report filed in August — and spent $1.22 million.

Money is more of a worry for Sheriff Ross Mirkarimi, who is being far outpaced in his re-election campaign by challenger Vicki Hennessy. The incumbent has raised $90,217 and spent $22,702.33. Hennessy has raised $244,639, of which she has spent $175,329.99.

Sheriff’s funds

But Mirkarimi had about $73,000 left in his campaign account on Sept. 19, compared with about $34,000 for Hennessy, whose $81,000 in cash-on-hand was offset by about $47,000 in unpaid bills.

The race for District Three supervisor has heated up in recent weeks, with appointed incumbent Julie Christensen pitted against former Supervisor Aaron Peskin. It’s an important race, both symbolically and politically. If Christensen loses the seat — which Lee named her to this year after David Chiu was elected to the Assembly — it will reflect poorly on the mayor. If Peskin wins, it will tip the balance of the Board of Supervisors toward the progressives.

So far, Peskin has outraised Christensen by nearly $60,000. He has collected $293,690.96 to Christensen’s $234,190.45. He has also spent less on his campaign, according to the finance report, leaving him with about $128,000 in his campaign war chest, compared to around $84,000 for Christensen.

A third candidate for the seat, educator Wilma Pang, did not file a campaign finance report, which is not required until a candidate has raised $1,000 or more.

Lizzie Johnson is a San Francisco Chronicle staff writer. E-mail: ljohnson@sfchronicle.com Twitter: @lizziejohnsonnn