After years of self-assured trampling over burdensome regulations and restrictive labor laws, Silicon Valley is belatedly paying the price for its aggressive, world-conquering disregard for the rules constraining its less open-minded peers. In the face of a series of lawsuits by their de facto employees, companies that make up the so-called sharing economy—Postmates, DoorDash, Uber, and the like—now find themselves on the defensive over the legion of “gig workers” that power the bulk of their profits. Though the practice of classifying workers as independent contractors rather than employees drew scrutiny almost as soon as it began, in recent years the litigious floodgates have opened, with Uber agreeing to pay a staggering $100 million to maintain its drivers’ classification (a settlement that was rejected in court); Lyft shelling out $27 million to do the same, and this Grubhub facing lawsuit to the same effect from its drivers, who claim the classification caused them to be underpaid.

Now, a driver for $800 million on-demand delivery start-up Postmates is making a similar complaint, filing a class-action suit against the company in San Francisco Superior Court last week. Amir Mostafavi, who is representing Postmates driver Melanie Anne Winns, acknowledged to me that “Postmates is neither the first nor the last employer to try to misclassify their employees by merely giving them the name of ‘independent contractor’ to decrease cost and increase profit. However, to use my favorite example in layman’s terms, you cannot call a dog a cat because a dog is not a cat.”

“The court will decide the classification of the class as employees or independent contractors after evidence and legal argument,” Mostafavi told me. (Winns’s suit also alleges that Postmates stole from its drivers, retaining some of the wages and gratuity they earned, and forced drivers to use direct deposit, charging them 15 cents per deposit to their bank accounts in violation with California labor law.) The lawsuit, he added, is intended to represent not only his client, but similarly situated Postmates drivers in California who feel they’ve been stiffed by the company.

In a statement, Postmates touted the benefits of its employees’ independent-contractor status. “While we do not comment on the specifics of pending litigation, we believe the flexibility Postmates exercise over how, if, and when they use the platform—reflects their independent contractor status,” the company said, adding that its platform “has enabled members of our fleet to supplement their incomes by more than $400M to date” and “stimulates growth for local economies by linking our network of customers and couriers to the brick-and-mortar merchants in their own communities.”

For Postmates and its fellow travelers, contract labor has been crucial in the quest to redefine the employer-employee relationship. Reflecting Postmates’ statement, start-ups tend to argue that their structure gives workers the freedom to set their own schedules—Uber, founder Travis Kalanick once argued, is less a full-time job and more “a way to fill in the gaps.” By choosing not to classify the people who earn income through their platforms as employees, however, companies forgo responsibility for costly benefits like sick days, overtime, Social Security, and health care. Additionally, contract workers are expected to provide their own cars and pay for related expenses, and they’re not subject to traditional legal protections.

Such companies sell themselves as platforms for services, rather than providers of those services—when Grubhub C.O.O. Stan Chia took the stand to defend Grubhub’s use of contractors, he argued that the company was not a food-delivery company, but “the premiere marketplace connecting diners with restaurants.” Similar logic has allowed Facebook to elide responsibility for news published on its site by labeling itself a content platform, and has blown the valuation of WeWork—which in former days would have been considered an office-leasing company—up to $20 billion, eight times that of a similar company that follows a traditional business model. But labor lawsuits like Winns’s threaten to dispel that illusion, bringing tech giants’ massively inflated values crashing back to earth.