Uber Technologies Inc. drivers seeking to be treated asemployees won a ruling that adds tens of thousands of them to thecase and may put hundreds of millions of dollars more at stake.

A judge's decision Wednesday that will likely let the vastmajority of Uber's 160,000 drivers in California join the case asit heads toward trial in June expands the company's liabilityexponentially, legal experts said. A victory for the driversthreatens to upend the ride share company's business model and cutinto its more than $60 billion valuation.

The drivers can now seek expense reimbursement, including asmuch as 57 1/2 cents for every mile driven, in addition to theirclaims for tips that are already part of the case, under the rulingby U.S. District Judge Edward Chen in San Francisco.