When California lawmakers passed a worker-protection bill essentially requiring Uber and Lyft to treat drivers as employees, it was thanks in part to a little-known group called Rideshare Drivers United.

Uber and Lyft had hoped for a deal with organized labor exempting them from the measure, and the Teamsters and the Service Employees International Union explored such an agreement. But Rideshare Drivers United, which represents more than 5,000 drivers in Southern California, fought the idea, speaking out for members who viewed it as a betrayal.

“From the beginning, they’ve been the voice of ride-share drivers not just in California but nationwide,” Assemblywoman Lorena Gonzalez, the bill’s author, said of Rideshare Drivers United. “Any union that wants to be the voice of ride-share drivers has to be inclusive of that group and others.”

Rideshare Drivers United is not a household name within the labor movement, or even a legally recognized union, and it represents only a fraction of drivers in California. But its growing clout challenges the notion that highly dispersed workers are nearly impossible to organize absent a deal with their employer or the state, which can come with strings attached.