Elizabeth Warren's presidential campaign is running a billboard in San Francisco calling for the breakup of the tech giants.

Warren has made challenging the power of the industry's largest players a key piece of her campaign.

The billboard is near a station for the rail line many tech workers use to commute to their jobs in the city.

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Elizabeth Warren is taking her message of breaking up the big-tech giants directly to those most affected by the companies.

The senator's presidential campaign has posted a billboard in San Francisco touting her stance against the industry's behemoths. The advertisement is half a block away from the city's main station for Caltrain, the commuter rail line many tech workers ride on their way to and from their jobs in the city or in Silicon Valley.

"Break up big tech," the sign reads, then asks people to text the campaign to "join our fight."

The campaign posted the ad days before Warren is slated to visit the Bay Area. She's scheduled to hold a town hall in Oakland on Friday and to appear at both the California Democratic Convention and a MoveOn event in San Francisco Saturday.

Warren campaign representative Saloni Sharma did not respond to questions about why the campaign decided to post the billboard with its particular message in San Francisco near the station. Instead, in an email, she echoed Warren's warning about the dangers of the big-tech companies.

"Today's big tech companies have too much power," Sharma said. She continued: "Elizabeth's plan would help ensure tech giants do not crowd out potential competitors, smother the next generation of great tech companies, and wield so much power that they can undermine our democracy."

Warren has made challenging the power of the tech giants a centerpiece of her campaign. She's called for breaking up the larger companies, including Facebook and Amazon, and more strictly regulating smaller ones.

Read this: Elizabeth Warren pulled a ninja move to turn tech angst into a crackdown with real teeth, and tech is going to suffer even if she's not president

It's unclear how Warren's message will play in San Francisco. The city and the Bay Area are ground zero for the tech industry and home to many of its largest companies, including Facebook, Google, and Apple. But the region has also suffered from many of the consequences of the industry's immense wealth, including sky-high housing costs, gridlocked traffic, overstuffed transit systems, and displacement of non-tech residents.

Such factors have led to a burbling backlash by some longtime residents against the tech industry.

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