A U.S. senator is calling on UPS to refund customers whose Christmas packages got caught up in widespread delays.

"In a very real sense, Christmas is on the line," Sen. Richard Blumenthal, D-Conn., said in a written statement Thursday. "I call on UPS to do the right thing and provide refunds to people whose Christmases were a little less cheery as a result of their late deliveries."

The senator said he recognizes the "tremendous work" that UPS, as well as the U.S. Postal Service and FedEx, put in this time of year. However, he said he was "disappointed" to learn so many people in his state and across the country were "left empty-handed" on Christmas.

Both UPS and FedEx were playing catch up Thursday after poor weather and overloaded systems delayed packages that were intended to be delivered in time for Christmas.

Neither company said how many packages were delayed but noted it was a small share of overall holiday shipments. But the problems appear to have affected many parts of the country.

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"We apologize that our customers did not receive their packages on Christmas," said Natalie Godwin, a spokeswoman for United Parcel Service Inc.

UPS did not make pickups or deliveries Wednesday. Extra workers were brought in Wednesday night to the company's hub in Louisville, Ky., to sort packages for Thursday and Friday delivery, according to Godwin.

Godwin said "UPS will honor its peak shipments commitments" to customers who used its air delivery service. Those shipping by ground have no guarantee past Dec. 11. Godwin said she didn't know if customers would receive refunds.

Between Thanksgiving and Christmas, FedEx handled 275 million shipments, according to Scott Fiedler, a spokesman for FedEx Corp. Those that were not delivered in time, Fiedler said, "would be very few."

"Our 300,000 team members delivered outstanding service during this holiday season, and we experienced no major service disruptions in the week before Christmas despite heavy volume," FedEx spokeswoman Parul Bajaj said in a statement Thursday. "Every single package is important to us, and we will continue to work directly with customers to address any isolated incidents."

Amazon.com has been notifying some customers affected by the UPS delays that it will refund any shipping charges and is giving them a $20 credit toward a future purchase.

Amazon spokeswoman Mary Osako said the company processed orders and got them to its shippers "on time for holiday delivery" and is now "reviewing the performance of the delivery carriers."

The Associated Press contributed to this report.