Contractors working for the Amazon Inc. Flex program load packages into vehicles to deliver to customers in San Francisco, California.Contractors working for the Amazon Inc. Flex program load packages into vehicles to deliver to customers in San Francisco.

Amazon is turning to its legions of contracted Flex drivers to deliver packages from mall-based retailers, allowing sellers to ship products from their own stores using the e-commerce giant's delivery service.

Amazon has been notifying Flex drivers in recent months that it is testing a new program where workers fetch packages from retailers in their area and drop them off at customers' doorsteps, according to a notice to drivers that was viewed by CNBC.

The notice says that Amazon is testing a retail delivery offer that will allow you to pick up and deliver pre-packaged orders from non-Amazon retail stores.

The notice was only sent to drivers in Las Vegas and only included orders placed at the Fashion Show Mall. It is not clear what stores are participating in the test.

The service is being tested in Tysons Corner, Virginia, as well as in Arizona and Arizona. According to a post on a popular group for Flex drivers, the company appears to be trialing the program in Friendswood, Texas, a city southeast of Houston.

Kate Kudrna, an Amazon spokeswoman, said that a few existing Amazon sellers are participating in the program and that Flex drivers can pick up orders from retail stores.

Kudrna said that they have been delivering from third-party stores for years.

Amazon Flex is a part of the company's fast-growing in-house logistics arm. The program uses everyday drivers to deliver packages in over 50 cities. They earn between $18 and $25 an hour, depending on the shift, and are responsible for costs like gas, tolls and car maintenance.

Amazon is trying to shuttle packages to customers at faster speeds. Amazon said it would spend $800 million over a three-month period to expand one-day shipping in the U.S. before the coronaviruses upended its fulfillment and delivery operations.

The company opened up its shipping and fulfillment network to other retailers, allowing them to apply Prime benefits to orders placed on their own sites.

There are other companies that offer fast delivery to retailers. DoorDash, Postmates, and Instacart are just a few of the delivery providers that have expanded beyond food and grocery.

As Prime One Day shipping expands, here's what it's like to be an Amazon Flex delivery driver.