UPS issued a service alert on Thursday morning saying the weather conditions around its regional hub in Philadelphia caused "a disruption to operations."
UPS said some shipments may experience "unavoidable delays."
RELATED: Nor'easter brings heavy snow, wintry mix to Philadelphia region
The company said contingency plans are in place.
UPS said it is working to move shipments as quickly as conditions permit.
The National Weather Service reported 6.3 inches of snow fell in the city -- the most since March 21, 2018.
[SERVICE UPDATE] Severe weather at PHL in Philadelphia, PA, may affect the transit time of some package and freight shipments. For updates, please track your shipments at https://t.co/k8NXG6YxCO— UPS (@UPS) December 17, 2020
Along with the nor'easter, UPS and other shipping companies are facing an unprecedented vaccine distribution and record breaking shipments.
An estimated 3 billion packages are expected to be delivered this holiday season around the country, according to ShipMatrix. Last year there were 2.2 billion.
UPS has been shipping 34 million packages a day.
The company told ABC News earlier this week, "Our in-house meteorology teams continues to monitor the weather and we'll make contingency plans."
Shipping expert Tim Kraft, an assistant professor of Operations and Supply Chain Management at NC State University, says to be prepared.
"The reality is that there's probably going to be some packages that either you sent or that you ordered online that just aren't going to be there on time for the holidays," Kraft said.
UPS and FedEx have suspended their money-back guarantees for on-time delivery.