Both companies blame the delays on an unprecedented surge in online sales and bad weather. UPS brought in extra workers to sort out the delayed packages.
"UPS apologizes to those customers whose packages were delayed. Our drivers are out making deliveries and pickups and we expect nearly all of the packages will be delivered today," UPS said in a statement. "We had additional operations at Worldport, the UPS international air hub in Louisville, Ky, on Christmas -- we are making every effort to get all packages delivered."
FedEx says it experienced no major service disruptions in the week before Christmas despite the heavy volume.
"Our 300,000 team members delivered outstanding service during this holiday season," FedEx said in a statement. "Every single package is important to us, and we will continue to work directly with customers to address any isolated incidents."