The measure would give Californians the ability to opt out of having their personal data sold or shared by requiring businesses to display a button on their websites that says, “Do Not Sell My Personal Information.” Clicking the link would take users to an opt-out form.

Mactaggart and his supporters seized on the recent controversy over Cambridge Analytica accessing the data of millions of Facebook users to benefit clients such as the Trump campaign, publicly calling on the company to stop opposing his ballot measure. There’s little reason to think it will.

Though Zuckerberg said on national television that Facebook has a “basic responsibility to protect people’s data,” his company has worked with other Internet giants to beat back numerous efforts to increase consumer privacy. They lobbied against federal legislation last year that would have required tech companies to obtain customers’ permission before selling their data to advertisers. And they lobbied against a bill in the California legislature that would have required Internet service providers to get permission from customers before selling or sharing information about their browsing history.

Now they’re fighting Mactaggart’s measure by warning that it would fundamentally disrupt the 21st Century economy, not only impacting the business of digital advertising, but also hampering many services people have come to rely on. Mapping apps, ride-hailing apps and email subscription services all rely on sharing users’ data. The initiative treats “sharing” data and “selling” data the same, and opponents say such services wouldn’t work if consumers were allowed to opt out of sharing the data. The measure says the opt-out wouldn’t apply when the consumer intentionally discloses personal information (for example, revealing their location when hailing a ride), but opponents maintain the distinction is unworkable.

“Just about every sector of business in the state will oppose this because it’s a direct threat to their vitality,” said Steve Maviglio, spokesman for the tech-funded political committee opposing the privacy initiative, called the Coalition to Protect California Jobs. The committee has backing from the California Chamber of Commerce, TechNet and the Internet Association — a trio of powerful and deep-pocketed interests.

Facebook didn’t respond to request for comment, but it’s a member of TechNet and the Internet Association, which argue that changing the Internet’s rules in one state is impractical because it’s a global network.

“This measure will stifle innovation and send companies to competing states and countries that do not have such job-crushing regulations,” said a statement from TechNet Vice President Andrea Deveau.

The initiative also would allow Californians to sue companies that violate their request not to share personal information — another point of contention for business groups, which almost always oppose policies making it easier for them to be sued.

Consumer groups have been assessing whether the initiative as drafted does what it aims to do. Several now support it, although others including the Electronic Frontier Foundation, which litigates civil liberties issues in technology, have not yet taken a position.

Leading the campaign with Mactaggart is Mary Ross, a former CIA analyst who moved to California two years ago. As a counterintelligence analyst, Ross said she helped monitor foreign governments’ efforts to spy on America. So when Mactaggart asked her to join his campaign, Ross said she had “an insider’s perspective” on the power of big data.

“Information is powerful whether it’s a government using it or a business,” Ross said.

“Information is being used to manipulate people and you don’t even know when you’re being manipulated ... Maybe it’s being done to make you buy something or maybe it’s being done to get you to go vote a certain way. But if there is no transparency or accountability, it’s going to continue.”

CALmatters.org is a nonprofit, nonpartisan media venture explaining California’s policies and politics.