For Amazon, getting packages to the door relies on every part of the shipping chain, and the company is stepping into the air cargo space. The online giant has at least 40 jets leased, and while the firm officially says they were only to help deal with extra holiday orders, there’s no question the move scares FedEx and UPS.

Amazon’s expansion into transportation is one of the firm’s most important maneuvers—it promises to help attract new customers and make good on fast shipping promises while keeping costs in check. Amazon’s jets fly to at least 10 airports around the country and help supply nearby warehouses, and almost all of them are flying nearly full, Reuters reports.

Differing from other cargo airlines, Amazon’s planes tend to fly later in the day and don’t stop at airport hubs to fill up, cutting shipping times to ensure quick delivery for Prime members. [Reuters]