Competing crises are slamming the U.S. Postal Service just days before Christmas, imperiling the delivery of millions of packages, as the agency contends with spiking coronavirus cases in its workforce, unprecedented volumes of e-commerce orders and the continuing fallout from a hobbled cost-cutting program launched by the postmaster general.

Nearly 19,000 of the agency’s 644,000 workers are under quarantine after testing positive for the virus or after a close exposure, according to the American Postal Workers Union. Meanwhile, packages have stacked up inside some postal facilities, leading employees to push them aside to create narrow walkways on shop floors.

Some processing plants are now refusing to accept new mail shipments. The backlogs are so pronounced that some managers have reached out to colleagues in hopes of diverting mail shipments to nearby facilities. But often, those places are full, too. Meanwhile, packages sit on trucks for days waiting for floor space to open so the loads can be sorted.

“[Customers] are screaming, ‘Where’s my package? Why did it go to Jacksonville, Fla., when it’s going to Miami?’ " said Martin Ramirez, president of the APWU Local 170 in Ohio. “I can’t speak on that. I’ve never seen this before where these places are overflowing.”

The end result: Many families won’t see online orders arrive in time for Christmas.

Through Dec. 12, the start of the Postal Service’s busiest period for package deliveries, parcel volume was up 14 percent compared with the same period in 2019, the agency told mailing industry officials. That surge has employees in some areas working upward of 80 hours a week, including some who have worked every day since Thanksgiving without a weekend. In Philadelphia, people are scheduled to work Christmas Day, said one mail carrier, who like others in this report spoke on the condition of anonymity to avoid retribution.

Mail performance has plummeted: Only 75.3 percent of first-class mail, such as letters and bills, arrived within the standard one- to three-day delivery window the week of Dec. 5, according to the most recent agency data available. This time last year, the mail service’s on-time score was closer to 95 percent.

Private express carriers, also inundated by package shipments, have stopped serving some retailers, sending more items through the Postal Service.

The agency is receiving as many as 6 million packages a day since FedEx and UPS enacted restrictions on large-volume retail shippers in early December, according to industry tracking firm ShipMatrix. For the week of Dec. 6, FedEx delivered 93.9 percent of its parcels on time, UPS delivered 96.1 percent, and the Postal Service, 87.5 percent. The agency’s drop in performance compared with the previous two-week period held up more than 3.5 million parcels by one or more days.

“Companies like FedEx and UPS have done some pretty dramatic things to limit the flow, the volume of packages through their system,” said Former Army secretary and GOP congressman John McHugh, chairman of the Package Coalition, an advocacy group made up of businesses and consumers that rely on the Postal Service for mail delivery. “Postal Service can’t and wouldn’t do that. They take on all comers. So you can well imagine that those are who are being turned away from FedEx, UPS and perhaps others are in all likelihood going to turn to the Postal Service.”

“This year can’t end fast enough,” said Jennifer Lemke, the clerk craft director at APWU Local 170 in northern Ohio.

Adding to the slowdowns is on-the-ground confusion over the cost-cutting initiatives that Postmaster General Louis DeJoy implemented during the summer and then paused at the direction of five federal courts. The Postal Service has appealed several of those rulings.

In the meantime, those battles have created uncertainty in the ranks about specific delivery procedures.

“No parcels are moving at all,” said one postal worker in Michigan, who spoke on the condition of anonymity because he was not authorized to comment publicly. “As bad as you think it is, it’s worse.”

While the perfect storm of crises is likely to delay millions of gifts and greeting cards, other more essential items, including prescription medications, bills and benefits checks also may be stuck in limbo. Mailing industry officials expressed worry that vaccine deliveries from private shipping companies could displace other packages and overwhelm parts of the mail system.

“We’re doing the very best we can,” APWU National President Mark Dimondstein said. “We know you appreciate that. This is a long, hard struggle. We’re asking for your patience, and no delayed gift should take away from the valuable family time and the reason people come together and celebrate. Hopefully everything will make it there on time. But if it doesn’t, it’ll still get there.”

Postal Service spokesman David Partenheimer said the agency is flexing its network to ensure that it is able to sort, process and deliver the mail despite staff shortages and capacity challenges. “Our entire Operations team, from collections, to processing to delivery, worked throughout this past weekend and continues to work around-the-clock to address the historic volume,” he wrote in an emailed statement.

The delays come after a tumultuous summer and election season. DeJoy, a former supply-chain logistics executive and major Republican financier, took office in June while the agency was projecting a major operating shortfall because of declines in first-class mail. DeJoy moved rapidly to cut costs and instituted a transportation schedule that cracked down on overtime and banned late and extra transportation and mail delivery trips.

Almost immediately, service suffered. A Postal Service inspector general report indicated that DeJoy and agency leaders did not analyze the effects of the new policies and did not consult the Postal Regulatory Commission about the changes, as multiple courts have held that the Postal Service was required by law to do. In the first five weeks of the policy, which was enacted in July and not rescinded until just before the November election, more than 7 percent of the nation’s first-class mail was delayed, according to a Senate investigation.

But packages have buoyed the agency’s finances. Parcel volume in May and June beat 2019 figures by 20 to 80 percent each week, staving off — at least temporarily — financial ruin. Mailing and package firms cheered those numbers, as well as market prognostications that e-commerce shopping habits elevated during the pandemic might endure beyond, injecting hundreds of millions of dollars permanently into the sector. The flood of holiday packages, though, appears to have pushed the mail system to the brink.

Retail analysts say that more than two years of e-commerce sales growth were crammed into 2020, starting in March when the pandemic took hold and surging again now. In the United States, online shopping sales are projected to reach $795 billion this year, up more than 30 percent from a year ago, according to research firm eMarketer.

“It boils down to too much of a good thing,” said Art Sackler, executive director of the Coalition for a 21st Century Postal Service, an industry group whose members include Amazon, eBay and other commercial mailers.

To ensure delivery by Friday, the Postal Service recommended allowing 10 days for retail ground service and making Wednesday the latest day for priority mail express service. But that’s still not a guarantee, and consumers across the country are reporting that orders placed as early as Nov. 27 are still not in hand.

Retailers have issued warnings to customers regarding shipping windows. In addition to a banner on Walmart’s website advertising “last call for pickup,” the big-box retailer’s most recent guidance for shipping cutoffs was issued on Dec. 15 for customers still shopping for gifts and groceries leading up to Christmas Eve.

Customers can book slots for pickup and delivery through Thursday, “pending availability,” on orders above $35 and dependent on local store availability. And express delivery within two hours is available, under the same conditions, for customers who order by 1 p.m. local time through Thursday. For free two-day delivery, customers had to have ordered by Saturday at 2 p.m. local time; for next-day delivery, the deadline was 2 p.m. Monday. In-store pickup on Thursday requires that the order be placed by 4 p.m. Wednesday.

T.J. Maxx issued some of the earliest shipping cutoffs among top retailers, saying on its website that standard ground shipping orders needed to be placed by Dec. 9 to ensure Christmas Eve delivery. The company did not respond to a request for comment.

Best Buy — which offers same-day delivery through Roadie, Shipt and Instacart — is enlisting store employees to drop off packages at customers’ homes daily until 10:30 p.m. in the run-up to Christmas.

In late November, Amazon designated cutoffs for Prime users hoping to make the Christmas deadline: Wednesday for one-day delivery and Thursday for same-day delivery. (Amazon founder and CEO Jeff Bezos owns The Washington Post.)

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

Other private mail carriers advised earlier cutoffs. UPS told customers to send their mail by Monday for three-day select delivery, Tuesday for second-day air delivery and Wednesday for next-day air delivery to arrive by Christmas Eve.

FedEx was more cautious with its estimated shipping: For domestic packages to arrive by Christmas Day, the firm listed Dec. 9 as the last day to ship through its SmartPost service and Dec. 15 for ground shipping. In a release, FedEx advised businesses to “refer to this calendar regularly and adjust order cutoff dates on your website as needed to help your customers avoid delays.” It suspended its money-back guarantee for customers shipping with express, ground, freight and office services until further notice.

In the meantime, some small-business owners are encouraging their customers to print out photos or PDFs of their ordered gifts to wrap and open on Christmas Day until the real thing arrives.

Some consumers whose packages are missing or have been listed “in transit” for more than a week, or have been offered refunds or reorders, are giving up on on-time delivery and instead sending money or gift cards, giving handmade presents, or shopping in stores.

“I mailed a package out,” said a Postal Service manager in central Florida, “and I’m trying to explain to my wife why the packages I mailed for her niece’s Christmas and birthday didn’t get there in time.”

With just days to go before Christmas and millions of packages caught in delivery limbo, many retailers are shifting their focus to same-day delivery and curbside pickup. Macy’s and Bloomingdale’s are partnering with restaurant delivery service DoorDash to get orders to shoppers’ front doors, while Sephora and Best Buy have similar arrangements with Instacart. Many others, including J.C. Penney, Kohl’s and World Market are offering discounts of as much as 20 percent to shoppers who pick up online orders curbside or in stores.

Abha Bhattarai contributed to this report.