By The CNN Business

More than 15,000 Amazon contract drivers (took legal action) against the e-commerce giant, alleging that Amazon (wrongly categorized) them as independent contractors instead of employees with minimum wage and overtime rights.

Millions of Americans participate in the “gig economy,” freelancing work through delivery and ride apps like Lyft, Uber, Doordash, and Instacart. But as gig work has gotten more popular, many of those workers say they are in fact employees, not just contractors, and therefore deserve more benefits and protections.

The definition and rights of a contract worker versus an employee, for example, has been fiercely debated in laws such as California’s Prop 22, which allows ride-hailing and delivery drivers to be treated as independent contractors with some added benefits, including a minimum earnings guarantee.

Amazon Flex, launched in 2015, allows independent contractors to sign up to deliver Amazon packages. Flex drivers provide Amazon Fresh grocery deliveries or same-day deliveries from the company’s warehouse hubs. Since the drivers are classified as independent contractors, these claims (ask for compensation) for unpaid wages and overtime, and reimbursement for expenses such as mileage and cell phone usage.

Lawyers for the case said in a statement that about 450 such claims had been previously filed with the American Arbitration Association.

Drivers from California, Massachusetts, and Illinois filed claims because laws about employee misclassification are “very clear” in those states, attorney Steven Tindall told CNN. The three states also allow workers to file claims for expense reimbursement from employers, Tindall added.

Tindall and another attorney, Joseph Sellers, have been collecting claims for years, Tindall said.

In a statement, Amazon said Flex “gives individuals the opportunity to set their own schedule and be their own boss, while earning competitive pay. We hear from most of the Amazon Flex delivery partners that they love the flexibility of the program, and we’re proud of the work they do on behalf of customers every day.” On its website, Amazon says most drivers earn between $18 to $25 an hour.

In their statement, Tindall and Sellers said Amazon only pays the drivers for a pre-determined “block.” If a Flex driver books a three-hour block on the app, they only get paid for three hours, even if deliveries come in that take more time.

Tindall told CNN that the workers filed independent arbitration claims instead of a class action lawsuit because drivers have to sign an agreement that forbids class action.

“Arbitration, unfortunately, limits the drivers’ pursuit of justice. So, we’re left with little choice but to file almost 16,000 individual arbitration actions at once,” Tindall said.