A former Uber driver in San Diego sued the ride-hailing company on Monday for racial discrimination in how it uses passengers' reviews to evaluate drivers.

The company relies on a star rating system, which the lawsuit says disproportionately leads to the firing of people who are not white or who speak with accents.

"Uber has long known that relying on a system that depends on passenger evaluation of drivers is discriminatory," wrote the driver's attorney, Shannon Liss-Riordan, in the federal lawsuit, which was filed in San Francisco and is seeking class-action status. The suit claims Uber fires drivers if their average ratings drop too low.

The suit aims to represent all minority Uber drivers who have been kicked off the app because of poor star ratings. It asks the court to order Uber to stop using passenger evaluations when deciding whether to ban drivers from the app.

"Uber's use of this system to determine driver terminations constitutes race discrimination, as it is widely recognized that customer evaluations of workers are frequently racially biased. Indeed, Uber itself has recognized the racial bias of its own customers," Liss-Riordan wrote in the suit.

Uber strongly contests this allegation. In a statement, the company called the suit "flimsy," arguing that "ridesharing has greatly reduced bias for both drivers and riders, who now have fairer, more equitable access to work and transportation than ever before."

An Uber spokesman would not comment on how passenger star ratings factor into a driver's termination. But the spokesman pointed out that when riders give a driver a low rating, the company asks for more information to determine if bias played any role.

The app asks passengers, after completing a ride, to rate their driver on a scale of 1 to 5. Uber says this system helps keeps rides safe by identifying problematic drivers.

In the suit, plaintiff Thomas Liu is described as Asian, from Hawaii and speaking with a slight accent. He claims he was fired in October 2015 after his average star rating fell below 4.6.

Liu contends that riders gave him bad reviews because of his race.

"He noticed riders [canceling] ride requests after he had already accepted the ride and the rider was able to view his picture. He also experienced riders asking where he was from in an unfriendly way," according to the suit.

Before Liu could file the federal lawsuit, he first had to file a discrimination complaint with the Equal Employment Opportunity Commission. It did not make a determination on his case and dismissed it in August, allowing him to pursue the claim in court.

The suit comes eight days before voters in California will decide the future of ride-hailing in the state.

A ballot initiative, known as Proposition 22, carves out an exception to a new state law that would force companies such as Uber to convert its drivers from independent contractors to employees.

Critics of Prop 22 say ride-hailing companies are attempting to avoid providing their drivers benefits such as paid sick leave, unemployment protection and health insurance.

Backers say drivers prefer flexibility over employee status. App-based companies Uber, Lyft, DoorDash and Instacart have pumped nearly $200 million to persuade voters to pass the proposition that effectively creates a legal loophole for ride-sharing and delivery companies.

Uber and Lyft have threatened to leave California altogether if the measure fails.

Last week, a state appeals court affirmed a lower court ruling that ride-sharing drivers are central to the companies' business and therefore should be afforded employee benefits.

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