United Parcel Service, coming off a successful holiday shopping season after suffering from a pileup in 2013, is still hard at work — the carrier now needs to process millions of returns.

UPS UPS on Friday said it expects to transport 4 million returned packages in the U.S. by the end of the first full week of January. On so-called “UPS National Returns Day,” which is Jan. 6, the company expects to ship more than 800,000 packages back to retailers and merchants.

“We have successfully completed two of three phases of the peak holiday delivery season,” said Alan Gershenhorn, UPS executive vice president and chief commercial officer. “We are now preparing for a surge in volume driven by Returns Week beginning next Monday.”

The shipping company has invested heavily in its infrastructure, building new facilities and hiring more temporary workers to meet rising demand for online orders as more shoppers flocked to the Internet to place orders for the holidays. A rush of orders is often seen just before Christmas, putting more pressure on retailers and shippers to meet demand.

And UPS said returns are also on the rise. The company’s research indicates that 62% of consumers polled in an online shopping study said they returned an item they bought online at some point this year. That’s up from 51% in 2012.

“As e-commerce continues to grow, simple returns services have become an essential part of the overall consumer shopping experience,” Gershenhorn said.