Amazon.com Inc. is being sued by three drivers, making the online retail giant the latest company to face legal action over the use of independent contractors in its delivery operation.

The proposed class-action lawsuit, filed Tuesday in federal court in Seattle by drivers for Amazon.com and Amazon Logistics Inc., alleges the company violated federal labor law by classifying them as contractors rather than employees. The drivers are seeking back wages, overtime pay and compensation for fuel, car maintenance and other expenses.

The lawsuit comes as Amazon is laying the groundwork for its own shipping business, which its executives have said will add delivery capacity, particularly during the peak holiday season. Amazon currently delivers its own packages from roughly 70 facilities, mostly built in the past two years, in 21 states.

The drivers named in the lawsuit have all driven for a program called Amazon Flex, a smartphone app launched last year, through which drivers choose the shifts they want to work and schedule their own pickups. The program has expanded to nearly 30 metropolitan areas.

The question of how to classify so-called “gig economy” workers has been roiling many of Silicon Valley’s on-demand services firms such as Uber Technologies Inc. and Postmates Inc., which say their workers tend to prefer to be independent contractors, because it allows for a more flexible schedule.