Pedestrians walk past a GrubHub Inc. banner on the exterior of the New York Stock Exchange (NYSE) in New York on April 4, 2014. (Jin Lee/Bloomberg)

A whole new branch of the sharing economy is coming under fire from disgruntled workers who argue that they're being treated like employees but are getting none of the workplace benefits.

Food-delivery services including GrubHub, Caviar and DoorDash were all sued Wednesday by drivers in San Francisco, who allege that the companies have "misclassified" them as independent contractors rather than formal employees.

The drivers argue in a class-action suit against GrubHub, for example, that the company didn't pay them overtime or minimum wage, or cover their fuel expenses as it should have if they were classified correctly. GrubHub spokeswoman Meghan Gage declined to comment on pending litigation.

Caviar and DoorDash did not immediately respond to a request for comment.

The suits against the on-demand food delivery services mark the next chapter in an ongoing battle between sharing-economy companies and some of the people who act as their laborers. Last month, a federal judge allowed a similar class-action lawsuit against Uber to move forward.

Whether companies like these have to meet employer obligations isn't just an ethical question — it could redefine the future of the industry. Reimbursing drivers for gas, mileage and tolls, a requirement for companies based in California, could cost Uber billions of dollars. And that doesn't even get into other benefits like retirement plans, disability insurance and the provision of other benefits.

But despite those costs, critics of the sharing economy say there should be a safety net for all workers in America, particularly as an uncertain job market drives people into freelance and part-time labor. How to regulate the sharing economy has even become a theme on the presidential campaign trail, where companies such as Uber and GrubHub are having an impact on a broader debate over the future of work.