Chris Jackson was halfway through his overnight shift sorting the mail for delivery when he and several colleagues were summoned into a windowless conference room.

The senior manager of the mail facility was there along with a representative from the union and other postal officials.

They confirmed the rumors that had been swirling all night. One of their colleagues in the Bethlehem, Pennsylvania, mail facility had been diagnosed with COVID-19.

They gave the staff the option of going home, and about half did. But the facility wasn't going to shut down. Instead, they set up cones around the area where the sick worker had been, and the overnight crew continued until dawn preparing the mail to be sent to people's homes.

"They said we need to have the delivery trucks out there," Jackson said. "They said delivery trucks really instill confidence that it's business as usual, that the mail is still getting to you."

Neither sleet nor snow -- nor the coronavirus. With tens of millions of people across huge swathes of the country on state-ordered lockdown, the mail has remained one of the few physical tethers to the wider world. Medicine, packages bought online, at-home coronavirus tests, even mail-in presidential ballots -- all require a reliable federal mail system.

But mail delivery requires a healthy workforce, and postal workers have been falling sick across the country -- Miami; Manhattan; Seattle; Portland, Oregon, and more have reported sick workers, according to Paul Hogrogian, national president of the National Postal Mail Handlers Union.

On Thursday, 13 postal workers had tested positive; by Friday, that number was 20, including the one from the Bethlehem facility where Jackson works, according to Hogrogian. On Sunday, postal officials in Washington said the number was "fewer than 30."

With a workforce of 630,000, those numbers are still relatively small, but they are expected to keep rising in the coming days and weeks. Jackson and other rank-and-file postal workers worry that the USPS isn't doing enough to protect them and that they could become unwitting carriers of the virus.

"They had no plan, and they weren't proactive at all," Jackson said. "It was just crazy to me."

FedEx and UPS workers are facing similar fears that their warehouses were contaminated or soon will be.

When Jackson returned to work the night after the meeting, he said the cones had been removed from the sick worker's station, and the crew was expected to keep going. Another Bethlehem colleague, Sean Craig, said he's continuing to report for work but is worried about his infant son and his 82-year-old mother.

"The concern is there just wasn't a plan in place," Craig said. "It was fly by the seat of your pants, which made me very angry."

Craig and his colleagues have the option of staying at home and using their sick days or vacation days if they feel uncomfortable working. One employee reported for duty at 10 p.m., learned that a colleague had fallen sick and was out the door by 10:30 p.m., Jackson said.

Those that stayed debated whether they should use their time now or bank their sick days in case things become even worse. Jackson reasoned that since he's 34, healthy and lives alone, he could afford the risk. "We haven't hit the peak yet, so let's work through this right now," he said, reflecting the view of some of his colleagues.

But he said he felt like the nonessential parts of his job should be jettisoned to focus on delivering important goods and products. "We're still sending brochures for cruise trips, thousands of them," he said. "This doesn't need to happen."

In a message to postal employees last week, Megan J. Brennan, the postmaster general, said that "there is no evidence the virus can spread through the mail." A recent study in The New England Journal of Medicine suggests that the virus disintegrates over the course of a day on cardboard.

But direct handling of the mail is only one aspect of the job inside postal facilities. Hundreds of people rotate through most warehouses, handling equipment, loading trucks, and preparing the mail to be delivered door to door by letter carriers who in turn fan out to homes across their area. That leaves plenty of opportunities to spread the disease, Jackson said, and there hasn't been enough planning or support.

"A lot of people asked, would they shut down the building for cleaning? Not an option," he said.

As for letter carriers who go door to door, new rules are quickly taking hold. Letter carriers walking up to people's doorsteps are instructed to "politely ask the customer to step back a safe distance" and to ask for their name instead of requesting their signature.

Hogrogian, the union president, said that he has been in direct conversation with senior postal officials about how to protect his people. The most glaring gap, he said, was that sometimes it took several days for officials to identify the people who had been in close contact with those who have tested positive.

"If they can't determine who's been in close contact for three or four days," he said, "that's three or four more days that employees are allowed to work."