Two California business interest groups and an anti-tax organization have banded together to oppose San Francisco’s Proposition C, the November ballot measure that taxes the city’s biggest corporations to fund housing and homelessness services.

The California Business Roundtable, the California Business Properties Association and the Howard Jarvis Taxpayers Association have filed court documents arguing that San Francisco officials shouldn’t have allowed the measure to pass with a simple majority vote, which they argue violates the state Constitution.

Prop. C passed in November with more than 61 percent of the vote, thanks to a broad coalition of supporters and a major jolt of publicity — plus financial backing — from Salesforce CEO Marc Benioff, who called the measure a moral imperative for addressing the city’s homelessness crisis.

But for decades, “special” taxes like the one Prop. C created — funds that are dedicated to a specific purpose — required a two-thirds supermajority to pass. The Howard Jarvis Association played an integral role in passing the two amendments to the state Constitution that set that standard: Propositions 13 and 218.

“There is no ambiguity in Props. 13 and 218. Voters clearly intended to require super-majority support for special taxes passed at the local level.” Rex Hime, president of the California Business Properties Association, said in a joint statement from the three organizations. “Prop. C is an illegal tax that violates decades of constitutionally protected taxpayer rights in California.”

But in 2017, a pivotal memo from the San Francisco city attorney’s office lowered the bar. The memo interpreted a state Supreme Court ruling from that same year to mean that ballot initiatives to raise taxes brought to the ballot by citizens — not government officials — required only a simple majority to pass.

At the heart of the court’s ruling in what’s known as the City of Upland case is the notion that ballot measures generated by citizens aren’t subject to the same constraints as those generated by local governments.

In San Francisco, three ballot measures to levy special taxes — including Prop. C — have been passed with a simple majority since the June 2018 election. All are facing legal challenges over the city’s use of that lower threshold.

In total, the measures will bring in up to $500 million annually for child care, teacher pay raises and homelessness services. But until the courts decide whether the city passed the measures legally, which is expected to take years, all of that money will be held in reserve: The city will collect the taxes, but none of it will be spent.

City Attorney Dennis Herrera has been steadfast in saying that his office will prevail in all three of the legal battles it now faces over the ballot measures and the threshold used to pass them.

The Howard Jarvis association is also leading the lawsuit against June’s Proposition C, which raises taxes on commercial rents to pay for child care services and early education. Proposition G, also from the June ballot, levies a $298 parcel tax for teacher pay raises. That measure is being challenged by Wayne Nowak, a San Francisco resident, with the backing of the multinational corporate law firm Greenberg Traurig.

“We are confident that when voters act through the initiative process, a simple majority vote is required,” said Herrera spokesman John Coté. “We look forward to defending San Francisco voters’ right to direct democracy and self-government.”

November’s Prop. C imposes an average of roughly 0.5 percent in gross receipts tax on corporate revenue above $50 million, impacting between 300 and 400 of the city’s biggest businesses. Hearst Corp., the parent company of The Chronicle, is subject to the tax. It’s estimated the measure will bring in between $250 million and $300 million annually for supportive housing, new shelters, mental health treatment and other services.

The measure inspired a fierce debate in San Francisco in the run-up to the November election. Opponents include Mayor London Breed, state Sen. Scott Wiener and Assemblyman David Chiu, who said the measure lacked the proper safeguards to ensure the money would be spent effectively. Prop. C’s supporters maintained that those politicians were bowing to the powerful business interests who railed against the measure.

Leaders of several San Francisco tech companies that would be subject to the tax came out against it, including Twitter and Square CEO Jack Dorsey and Stripe CEO Patrick Collison.

No companies appear to have signed on to the legal proceedings directly, according to court documents. The California Business Roundtable’s membership, however, includes major companies like Wells Fargo, Chevron and Comcast. Both the business roundtable and the California Business Properties Association are also parties in the lawsuit against the city over June’s Prop. C.

“San Franciscans are ready to see visible progress and real solutions to our homelessness crisis,” said Christin Evans, one of the main proponents of November’s Prop. C and a small-business owner in the city. A legal challenge, she added, “only delays real solutions, endangers lives and opposes the will of a majority of San Franciscans.”

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa