(NEW YORK) -- A massive winter storm could cause delivery delays ahead of Christmas, with blizzard conditions impacting major shipping hubs and post offices in parts of the United States.
"Significant weather events" are affecting UPS air and ground services, including UPS hubs in Louisville, Kentucky, and Rockford, Illinois, the company said Friday.
"As a result, some delivery and pickup services in these areas will be affected," UPS said in a statement. "We will work to ensure the safety of our employees while minimizing effects on service. Contingency plans are in place to help ensure that shipments arrive at their final destinations as quickly as conditions permit."
FedEx has also experienced "substantial disruptions" at its hubs in Indianapolis and Memphis, Tennessee, due to severe winter weather that has "created potentially hazardous operating conditions."
As a result, packages committed to being delivered by Friday and Saturday could potentially be delayed, the company said.
"We recognize the importance of deliveries this holiday weekend," FedEx said in a statement Friday. "Contingency plans are in place, and we are prepared to provide the best possible service as conditions allow."
Severe weather has forced nearly 90 United States Postal Service locations to temporarily close as of midday Friday, according to the agency's service alerts, including 53 in South Dakota and 20 in North Dakota. Iowa, Minnesota and Nebraska are each reporting a handful or so locations that are temporarily closed due to weather.
"Generally, we will continue to attempt all deliveries where accessible and safe to do so," USPS said in a statement Friday.
The agency is urging people to clear snow and ice from their sidewalks, stairs, porches and mailboxes and maintain a clear path to their mailbox to aid letter carriers during wintry weather.
Amazon has also temporarily closed sites in impacted areas "out of an abundance of caution," Amazon spokesperson Barbara Agrait said.
"The health and safety of our employees, customers and the drivers who deliver packages is our top priority which is why we continually monitor weather reports and adjust operations as needed," Agrait said.
ABC News' Yoni Mintz contributed to this report.