This story has been updated.

A historic crush of e-commerce packages is threatening to overwhelm U.S. Postal Service operations just weeks before Christmas and runoff elections in Georgia that will decide control of the U.S. Senate, according to agency employees and postal industry tracking firms.

As Americans increasingly shop online because of the coronavirus pandemic, private express carriers FedEx and UPS have cut off new deliveries for some retailers, sending massive volumes of packages ordered past deadlines to the Postal Service.

That has led to widespread delays and pushed the nation’s mail agency to the brink. Postal employees are reporting mail and package backlogs across the country, and working vast amounts of overtime hours that have depleted morale during another surge of coronavirus infections nationwide.

“We’re really gridlocked all over the place,” said a Postal Service transportation manager in Ohio, who like others in this report spoke on the condition of anonymity to avoid retribution. “It’s bad. I’ve never seen it like this before.

“UPS and FedEx have shut us off. Nobody can keep up right now, but we don’t have the luxury of turning people down. They’re sitting on so much mail right now that it’s almost one day at a time in these facilities.”

A letter carrier in Detroit reported that colleagues around the city were assigned two eight-hour routes each day last week to make up for missing employees and pallets full of undelivered boxes. In the first two weeks of December, nearly one of every five work hours within the entire agency was an overtime hour, according to public payroll data.

A letter carrier in Philadelphia said supervisors were rerouting employees to facilities all over the city to dig out from growing backlogs.

“I don’t think anyone, including the post office itself, knows just how bad delays are,” the Philadelphia carrier said.

The agency, which shared a news release on Monday night in response to a request for comment, is bracing for even more volume. It warned employees in a statement, “Peak season to peak this week.”

“We thank our customers for their continued support, and we are committed to making sure gifts and cards are delivered on time to celebrate the holidays,” Kristin Seaver, chief retail and delivery officer of the Postal Service, said in the release. “We continue to flex our network including making sure the right equipment is available to sort, process and deliver a historic volume of mail and packages this holiday season.”

E-commerce sales are expected to reach $189 billion in November and December, according to research by Adobe Analytics, up 33 percent compared with the same period a year ago.

To prepare for the influx, some retailers have advertised shipping deadlines to encourage customers to make their purchases early and allow ample time for packages to arrive by Christmas Day. The Postal Service encouraged customers to do the same, and hired more than 50,000 seasonal workers, added transportation and packaging tracking, and expanded Sunday deliveries for cities with especially high volumes, the agency wrote in a statement.

But the tidal wave appears to have caused delays even in the delivery of first-class mail, such as letters and bills. The Postal Service told Congress that only 78.9 percent of first-class mail was delivered on time during the week of Nov. 28, well below its internal goal of 96 percent. (The agency reports performance data on a two-week delay to more accurately process the figures.)

The Postal Service logged 94.8 percent of packages through handheld bar code scanners that track an item’s progress through the mail system from receipt to delivery. But a Washington Post investigation in October found that postal workers and supervisors routinely falsify those scans — one of few package-related performance statistics the agency makes public — to boost performance statistics.

Commercial delivery services including Amazon, UPS and FedEx rely on the Postal Service for the “last mile” shipping of its packages to save money, or ensure delivery on Sundays or to rural areas. Those packages frequently end up in the same delivery trucks carrying other mail processed through the Postal Service, which could contribute to delays. (Jeff Bezos, the founder and chief executive of Amazon, owns The Post.)

The wave of online shopping during the coronavirus pandemic forced Amazon to grow and adapt its logistics operations. (The Washington Post)

Postal analytics firm Late Shipment wrote in a 2020 holiday shipping report that massive hiring sprees from private shipping firms will not be sufficient to combat expected delays. From April through October, packages shipped through FedEx and UPS’s express delivery services nationwide were delayed at rates on par with or higher than during the 2019 holiday season.

UPS hired 100,000 seasonal workers, added new facilities and aircraft, and expanded weekend delivery to plan for the peak season, the company said in a recent news release.

“UPS is running one of the most successful peak holiday shipping seasons ever,” chief executive Carol B. Tomé said in the release. “With great discipline and precision, we are delivering industry-leading on-time delivery performance — all part of our focus on ensuring we maintain a reliable delivery network that all of our customers can depend on.”

FedEx spokesman John Scruggs said in an email that the company expects an “unprecedented surge” in mail this season.

“Delivery drivers, warehouse employees, and support staff across the globe are tirelessly and safely working to meet the surge in demand this holiday season on top of volume increases created by the COVID-19 pandemic,” Scruggs said, noting that FedEx has hired more than 70,000 seasonal workers, moved to seven-day operations, sped up Sunday delivery and is proactively working with customers.

Former Army secretary and GOP congressman John M. McHugh, chairman of the Package Coalition, an advocacy group made up of businesses and consumers that rely on the Postal Service for mail delivery, said the agency should be positioned to accommodate the influx of mail.

“Any commercial interest that mails packages to their customers wants those customers to be happy and receive packages on time,” he said. “Everybody is doing their best to try to accommodate this. There’s a reality, though, that the increase that has been seen in the package industry, writ large, was really planned for over the next three or five years instead of the next three or five months. It’s a real conundrum to have that much growth in that period.”

The package delays come after a tumultuous summer and election season for the Postal Service, in which the agency struggled to implement cost-cutting measures imposed by Postmaster General Louis DeJoy, then had to roll them back while more than 65 million Americans voted by mail in the November election.

Now the immense package volumes threaten to snarl postal operations in Georgia amid runoff elections for both of the state’s Senate seats. Long a Republican stronghold, Democrats hope both races are in play after Republican senators Kelly Loeffler and David Purdue were embroiled in ethics investigations. Neither received 50 percent of the vote during the November election, pushing the races to a decisive runoff.

Already, more than 1.2 million voters have requested mail-in ballots in Georgia, according to the U.S. Elections Project, and more than 260,000 ballots have been returned, including more than 100,000 through the Postal Service, the mail agency reported in federal court.

Since Nov. 28, it has processed 74.5 percent of those ballots on time, but only 68.2 percent on the six days when it processed at least 10,000 ballots.

On Monday, DeJoy released a video message thanking Postal Service employees for their work during the holiday season.

“We are expecting record package volume this season, possibly a third more than last year,” he said in the video. “Our competitors are likely to get more volume than they can handle, which means we may be getting a lot of overflow.”

DeJoy added that the Postal Service is experiencing high rates of absenteeism among workers in locations where coronavirus infections are surging, which puts a strain on the system’s processing.

He said that “2020 has been a difficult year for the nation and for the Postal Service. The women and men of the Postal Service have played a tremendous role in supporting the nation throughout the pandemic, during the election season, and now through a very busy holiday season. I am grateful for your service in every community.”