FedEx Corp. and the U.S. Postal Service said today they have extended through September 2024 an existing seven-year contract for FedEx's air and international unit to transport USPS packages.

The agreement adds four years to the current compact, which was signed in 2013 and up for renewal in 2020.

FedEx Express, the unit of Memphis-based FedEx, provides airport-to-airport deliveries of USPS' "Priority Mail Express" and "Priority Mail" products, under which USPS provides one- to three-day deliveries of packages across the U.S. The contract generates about $1.5 billion in annual revenue for the FedEx unit.

The FedEx-USPS relationship dates back to 2001, and the contract has been renewed twice since then. The original contract stirred controversy after FedEx's rivals claimed that there was no competitive bidding in the process. Since then, however, the contract has been automatically renewed.