In a last-minute move, FedEx boosted its staffing on Friday to deliver packages when it absolutely, positively had to be there by Christmas.

The shipping giant announced it would deliver packages on Christmas Day and open counters at its Express offices across the U.S. so customers can pick up their gifts themselves.

Still, many angry customers vented their frustration over the late deliveries on Twitter, using the hashtag #FedExFail.

The carrier blames the delayed shipments on rough weather across much of the U.S. and a last-minute surge of holiday shopping. "We are continuing to make adjustments and do everything we can to minimize impact on our customers,” a spokeswoman told The Wall Street Journal.

Rival UPS told the newspaper its operations were running smoothly.

The counters at FedEx offices were scheduled to stay open Friday from 9 a.m. to 1 p.m. The company's other offices were closed.

Household deliveries were given top priority on Friday.

Customers can find out if their delayed shipment is scheduled for Christmas day delivery or available for pick up by checking at fedex.com or calling 800-463-3339.

The Associated Press contributed to this report.