Those planning to head to the post office to send out holiday cards and packages should brace themselves for longer lines if they go on Dec. 14.

That’s when the U.S. Postal Service expects to have its busiest mailing and shipping day of the year. The Postal Service also predicts that date, which falls on a Monday, will draw more than 7 million visitors to its website, usps.com, marking its busiest day online as well.

Throughout the holiday season, the Postal Service expects to deliver about 15.5 billion cards, letters, and packages. About 600 million packages alone will be delivered between Thanksgiving and New Year’s Eve, Postal Service officials predict, up nearly 11 percent from last year.

While Dec. 14 will be the busiest day for mailing, Dec. 21 is expected to be the busiest day for delivering holiday cards, letters and packages. More than 30 million packages are expected to be delivered by the Postal Service on that day alone.

About 30,000 additional Postal Service employees are being hired nationwide for the holiday season to meet the demand, officials said.

“Customers can count on the Postal Service and our more than 600,000 dedicated employees to deliver their holiday gifts, cards and letters,” Postmaster General and CEO Megan Brennan said in a statement. “We have been investing in our infrastructure, including package sortation equipment, new delivery vehicles and scanning technology to expand our capacity, improve operating efficiency and provide real-time visibility.”

Despite seeing an annual surge in demand every year around this time, the Postal Service continues to struggle financially as its costs of doing business outweigh its revenue. Last month it reported a net loss of $5.1 billion for its 2015 fiscal year that ended Sept. 30, down slightly from the $5.5 billion loss is had in 2014.

The Postal Service relies on the sale of postage, product, and services to fund its operations. It receives no tax dollars for operating expenses.

UPS, one of its main competitors, expects to deliver a record number of holiday shipments this year and to have its busiest day on Dec. 22.

UPS officials said the company anticipates delivering more than 630 million packages between Black Friday and New Year’s Eve, up more than 10 percent from last year.

Of those, about 36 million packages will be delivered by UPS on Dec. 22 alone, up from 35 million on the company’s busiest day last year and more than double the normal daily average of 18 million deliveries, according to UPS.

UPS is benefiting as more consumers opt to shop online, officials said. Third-party shipping companies like UPS and FedEx, for instance, ship the orders processed via various online sites, including retail giant Amazon.com.

“Consumer preference for online commerce is driving tremendous growth opportunities for UPS,” Executive Vice President and Chief Commercial Officer Alan Gershenhorn said in a statement.

“UPS has dedicated people around the world that are ready to ensure e-commerce, multi-channel and traditional shoppers are served on time during the holidays,” he said. “We are ready to help our customers take full advantage of the holiday season.”