PHOENIX -- Monday is expected to be the busiest mailing day of the year, according to the United States Postal Service.
With a projected 420 million packages to deliver, it's crunch time for postal workers.
3TV got a sneak peek Thursday night at the inside of the Phoenix West Valley Logistics and Distribution Center, a hub for the region and the largest distribution center in the nation.
The facility has nearly 900 employees working overnight, including 200 temporary workers hired for the holiday season.
"They're like little elves in there, moving mail around to get it out the next day," said spokeswoman Julie Utley. "They know people depend on us getting packages there on time."
USPS expects a 12 percent increase over last year, partly as a result of more people buying gifts online.
In total, the Postal Service expects to deliver nearly 15 billion letters, cards and packages from Thanksgiving to New Year's Eve.
Here are some important deadlines to know:
Friday, Dec. 20: Deadline for sending first-class mail
Saturday, Dec. 21: Deadline for priority mail
Monday, Dec. 23: Deadline for sending priority mail express
Wednesday, Dec. 18: Busiest delivery day for cards and letters
Thursday, Dec. 19: Busiest delivery day for packages
Tuesday, Dec. 24: Normal delivery day, but most post offices will close at noon.
For more information, visit www.USPS.com.