"We're sorry that there could be delays and we're contacting affected customers who have shipments available for pickup," said Scott Fiedler, a spokesman for FedEx Corp.
Between Thanksgiving and Christmas, FedEx handled 275 million shipments, according to Fiedler. Those that were not delivered in time, he said, "would be very few."
Three people told The Associated Press that when they tracked their packages online, FedEx said deliveries to their homes were attempted but failed because "the business was closed." During follow-up calls with customer service, they said they learned that the local depot was overwhelmed and didn't attempt delivery.
On Sunday, Eric Swanson ordered a doll for his daughter and a sweater for his wife through Amazon.com and one of its affiliated sites. As an Amazon Prime customer, there was a promise of two-day delivery, getting the gifts to his Carmichael, Calif. home just in time for Christmas. One was shipped via UPS, the other FedEx.
"I thought it would happen," Swanson said. Online tracking tools said the packages would arrive by 8 p.m. Tuesday. Neither did.
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."
While some customers may get money back, they might think twice about ordering online next year.
"My wife understands but my 5-year-old daughter ... I think we're going to let it be a surprise when it comes," Swanson said. "Next time, if I need to get a gift and cut it that close, I will just have to enter the fray and go to the mall."
Scott Mayerowitz can be reached at http://twitter.com/GlobeTrotScott.