UPS is a little behind schedule after last week's surge in online orders.
"This is, after all, the third consecutive year in which Cyber Monday purchases have overwhelmed the company's capacity to deliver packages for the holidays", Teamsters General President James Hoffa wrote in a letter to UPS Chief Executive Officer David Abney on Monday.
The delays came in spite of UPS making massive investments in its network, technology and facilities over the past few years, following a disastrous 2013 holiday season, and again hiring 95,000 temporary workers.
The company says deliveries should be back on track by the end of the day Wednesday and it still expects most packages shipped between Thanksgiving and Christmas to arrive on time.
The Atlanta company is sticking with its forecast of holiday shipments of more than 750 million package deliveries between Thanksgiving and December 31, a 5 percent increase over past year.
United Parcel Service on Tuesday said customers should expect some delays this week as the delivery service struggles with an influx of holiday shipments. The company said Cyber Monday was the single biggest shopping day in Amazon's history, surpassing this summer's Prime Day 2017.
In addition, UPS told over 100 delivery centers in areas that have high demand that their drivers might be requested to work more hours until January 5, including as many as 70 hours over a period of eight days. By comparison, FedEx's express service scored better than 94 percent. The company notes that more shoppers were doing their Christmas buying then than what it was previously expecting.
The challenges during the holiday season have been increased due to the improved economy making it much harder for UPS, FedEx and other delivery companies to find the additional seasonal help necessary. However, it wasn't ready for the amount of orders that were made around Cyber Monday.
The company tries to prevent just this type of bulge in volume by working with retailers and adding surcharges to discourage too many shipments on the busiest days.
Shares of UPS fell $3.35, or 2.7 percent, to close at $120.37.