James Martin/CNET

Uber's headquarters in San Francisco was the scene of a commotion on Monday. As police escorted dozens of US mayors into the ride-hailing service's luxury offices for a tour, tens of protesters shouted "shame" at the lawmakers. Meanwhile, a line of taxis slowly drove by honking their horns in support of the protesters.

The mayors were in San Francisco for the four-day US Conference of Mayors, which brought together nearly 300 mayors to discuss local policies and politics. The protesters were mostly members the San Francisco Taxi Workers Alliance, a local cabbie union, who were there to demand ride-hailing companies be regulated the same way as taxis.

"We are trying to make our voices heard by the mayors," said Chakib Ayadi, a SFTWA board member who helped organize the protest. "I just want [ride-hailing companies] to be regulated and on the same playing field as us. I'd be very happy to compete with them that way."

Taxi drivers have long had beef with Uber dipping into their customer base. Over the past couple of years, cabbie protests have erupted in major cities across the world -- from London to New York to Mexico City. Taxi drivers say that not only are ride-hailing companies stealing their business, but the companies also don't play by the same rules with the driver insurance and background checks they require.

Uber is a service that lets passengers in need of a ride hail a driver with a smartphone app. Since the company was founded in 2009, it's gone from operating just in San Francisco to being in hundreds of cities in 57 countries. It's also become the second-highest valued venture-backed company in the world with a valuation of $41.2 billion.

Uber and its rival Lyft were sponsors of this year's US Conference of Mayors, which also hosted President Barack Obama and Democratic presidential candidate Hillary Clinton. As conference sponsors, the companies' drivers shuttled attendees around the city and Uber gave the mayors a tour of its headquarters.

James Martin/CNET

Uber spokeswoman Eva Behrend said that mayors widely support ride-hailing apps and that "nearly 50 jurisdictions across the country have adopted regulations that embrace ridesharing."

"In just five years, Uber has made a significant impact on local communities by delivering reliable and affordable options, helping to create tens of thousands of economic opportunities, reducing DUI rates, and increasing access to underserved neighborhoods," Behrend said.

But several city mayors have also had their issues with ride-hailing companies. Houston Mayor Annise Parker wrote a letter to Uber in April saying the company must require Houston drivers to get city licenses or be shut down. And Madison, Wis., Mayor Paul Soglin has advocated for mayors across the US to more tightly regulate ride-hailing companies.

The San Francisco Municipal Transportation Agency released a report last September that said ride-hailing companies were sinking the city's taxi businesses. Cab use had decreased by 65 percent over the previous year, according to the report. Taxi drivers at Monday's protest echoed these same concerns.

"I'm sick and tired of losing all my money," said Mike Gardelle, who has been a taxi driver in San Francisco for three years. "I'm working twice as hard for half the money."

Gardelle said that when he started driving a taxi he made between $290 and $300 a day, and now he's lucky to take home $100. Another protester, Robert Cesana, has been a San Francisco taxi driver for 30 years and said his wages have also plummeted.

"I turn 78 this month, and my livelihood is in enormous danger," Cesana said. He said he's trying to sell his once-coveted taxi medallion to another qualified driver with a cab license. "But since Uber moved into the city, nobody wants to buy it."

Uber also came under scrutiny from the privacy advocacy group Electronic Privacy Information Center on Monday. The group filed a complaint against the ride-hailing company with the Federal Trade Commission, asking the agency to investigate Uber's privacy practices, along with how it collects user data.

Uber updated its privacy policy in May to make it "easier to understand" and also clarify that it can access passengers' location data even when they're not actively using the app. This new policy is slated to go into effect July 15.

CNET's Brett Murphy contributed to this report.