San Francisco Mayor London Breed’s elaborate proposal to unlock some of the money raised by Proposition C — the November ballot measure taxing big businesses to fund homelessness programs — sailed unanimously through the Board of Supervisors’ budget subcommittee Wednesday.

The first Prop. C payments should begin flowing into the city’s coffers this month. Back in January, Breed introduced an ordinance that would give companies subject to Prop. C a tax break if they agree to let the city keep the money they pay — even if the courts strike down the measure and order the funds to be repaid.

Voters passed Prop. C by more than 61 percent in November, creating a tax on the city’s biggest businesses that would bring in between $250 million and $300 million annually for supportive housing and homelessness services. Hearst Corp., the parent company of The Chronicle, is subject to the tax. But the city will not spend the money until a prickly legal dispute over the measure’s margin of victory gets resolved. Breed opposed Prop. C in the run-up to election day.

If the courts rule against the city, the tax would be invalidated, compelling the city to return the money it collected. Breed’s proposal, co-sponsored by Supervisor Vallie Brown, would allow companies to pay some or all of their Prop. C tax bill and waive their right to have the money returned if the courts rule against the city.

In return, the companies would get a 10 percent tax break on the money they let the city hold onto. The tax break would last until the legal issues resolve or until 2023, whichever comes first.

“Funds are sitting in a bank account while people on our street suffer,” Andres Power, the mayor’s policy director, told the subcommittee Wednesday. “Ninety cents today is better than a dollar in three years time.”

Whether a 10 percent tax credit will be enough of an incentive for big corporations to abandon money they could otherwise win back remains to be seen. Power said the administration had been meeting with numerous companies about the proposal, but no one has yet agreed to participate in the program. The Board of Supervisors will take up the ordinance next week.

— Dominic Fracassa

Email: cityinsider@sfchronicle.com, dfracassa@sfchronicle.com Twitter: @sfcityinsider @dominicfracassa