The delivery company says some packages may be arriving one to two days late, because of the surge in online orders.
UPS says the backlog impacts just a small percentage of packages, and is hoping to be back on track by the end of Wednesday.
The company shifted more workers and resources to the areas that saw a huge spike in shipped packages.
UPS expects to deliver 750 million packages during the holiday season, up 5 percent from its holiday volume in 2016.