Opponents of Airbnb rally before a hearing called Thomson Reuters The biggest money in San Francisco politics right now is coming from one company: Airbnb.

The housing rental site has put up more than $8 million to fight a ballot initiative that would put strict restrictions on the city's short term rentals, according to campaign contribution filings.

In comparison, the largest contributor to the opposition's campaign is a hotel labor union that donated $125,000.

That's a lot of money to spend on politicking, even in the tech world — for instance, Google spent $16 million on lobbying the federal government in 2014.

The two sides are battling over Proposition F, a ballot initiative that wants to restrict the number of nights a person can rent out their home and fine companies like Airbnb if they list any rentals not registered with the city. (That's the short version — the full ballot initiative is here, along with a breakdown)

Airbnb has vehemently opposed any plan to fork over its data and curb housing nights. To do so, it's donated $8,148,721 to its committee, the aptly named "San Francisco for Everyone: No on the Home Sharing Ban, Sponsored and Major Funding by Airbnb".

As of the September 19 funding records, Airbnb had only donated $3.3 million, as shown in the chart below:

Two subsequent donations in the past week boosted the total to over $8 million.

While San Francisco is already plastered in billboards and advertising to say no to Prop F, the committee still has a lot of cash to burn through before November's election. It has only spent $3.6 million so far.

Airbnb, for its part, is happy to pour money into opposing it. It is a threat to its business and in its backyard.

"Our community is committed to defeating Proposition F, an extreme measure that circumvents the short-term rental regulations passed by the Mayor and Board of Supervisors last year," an Airbnb spokesperson told Business Insider. "This measure will hurt San Francisco neighborhood merchants, local tourism and the thousands of middle class people relying on home sharing to help make ends meet."