Amazon has already become the most dominant online retailer, and it's poised to take over the delivery space next. The ecommerce giant announced the launch of its Buy with Prime program on Thursday; the service provides third-party retailers access to the company's extensive shipping and fulfillment network, even for orders on non-Amazon sites.

Retailers using the service will have the option to attach the Prime icon to items on their website that are eligible for free two-day or next-day delivery. Additionally, Prime members will be able to use the payment and shipping information associated with their Amazon accounts to place an order. It's a major opportunity for Amazon to cash in, as sellers will pay various fees for payment processing, fulfillment, storage and more.

But Buy with Prime isn't available to all retailers just yet; for now, only sellers who use Fulfillment by Amazon (FBA) can take advantage, by invitation only. Ultimately, the company does plan to expand to include other merchants, which has the potential to level the company even further up in the online-delivery game — potentially far past UPS, FedEx and even the U.S. Postal Service.

Currently, Amazon offers a Multi-Channel Fulfillment program to allow sellers to store and ship goods with Amazon's services via third-party sites.

Buy with Prime is the company's latest move in a long-running campaign to maximize profit with its sprawling shipping and logistics operations. According to a report from the company, third-party seller services, including comissions, fulfillment and shipping fees and other services, climbed 11% year over year to $30.3 billion in the most recent quarter.