[UPDATED at 4:30 p.m. ET on March 13]

Federal prison union officials and inmate advocates warn that the combination of chronic understaffing, a new leave policy and the realities of coronavirus quarantines could lead to the first nationwide federal prison lockdown since 1995.

As coronavirus races across the country, staffing challenges are particularly complicated in the nation’s jails and prisons where conditions create a tinderbox for contagion. There is no such thing as teleworking for a correctional officer tasked with guarding inmates.

Union leaders for the Council of Prison Locals worry that existing low staffing levels in federal detention centers and prisons — which have required teachers and other social workers to fill in for correctional officers in the past — will exacerbate the impact of losing staff members to quarantines for coronavirus infections.

The federal prison system, which houses nearly 175,000 inmates, represents only a fraction of the overall prison and jail complex in the United States. More than 2.2 million people throughout the country are estimated to be behind bars. Though small by comparison, the federal system sheds light on issues many state, county and local officials are grappling with now. Because the facilities are typically dense and crowded, they could become prime breeding grounds for the highly contagious coronavirus.

If the coronavirus begins to spread rapidly among staff and inmates, it could prompt a nationwide prison lockdown at federal sites, said Aaron McGlothin, head of the prison staffers’ local union at Federal Correctional Institution-Mendota near Fresno, California.

“You’ve got to understand we’re in a prison — there’s nowhere to go,” he stressed. “If somebody comes down sick, what are you going to do? Everybody’s going to get sick.”

The Federal Bureau of Prisons said there have been no confirmed coronavirus cases in its 122 facilities as of March 10. But Joe Rojas, the union’s Southeast regional vice president, said there have been scares in federal facilities in Seattle and Miami. The bureau told staff Friday it was canceling visitation for 30 days, according to plans seen by KHN that were first reported by the Associated Press. Legal visits, inmate transfers and staff travel are also suspended for 30 days. In areas where community transmission of coronavirus is high, the bureau said it will enhance screening for staff, including temperature checks. The state corrections departments in Florida, California and Colorado all said earlier in the week they are cutting off visitation to inmates at their sites.

Worldwide, prisons have become a flashpoint amid this rapidly escalating public health crisis. Iran temporarily released 70,000 prisoners to combat the spread of the novel coronavirus within jails, while Italy is facing prison riots over lockdown conditions that have led to at least 50 inmate escapes and six deaths.

In the U.S., union officials are questioning a federal Bureau of Prisons leave policy issued Monday in an internal memo obtained by Kaiser Health News that says staff who contract the coronavirus and are symptomatic must use sick leave to self-quarantine. The memo said it followsguidance from the U.S. Office of Personnel Management, which advises the federal government workforce on leave policies.

Union officials said the policy discourages those who have the virus from staying home for the full duration of the illness. Federal prison employees receive four hours of sick leave every two weeks, amounting to about 13 days a year. But the Centers for Disease Control and Prevention recommends 14 days of isolation for those who only have been exposed and says those who are sick should remain quarantined until cleared by a public health official, which could be far longer.

That means most federal prison employees would need to borrow time they had not yet accrued if they do get sick. And even then, it might not cover the full time needed to get better and no longer be contagious.

“I wouldn’t want to give them any excuse or reason to come back in before they’re ready,” said Rick Heldreth, the local union president of West Virginia’s Hazelton.

That’s in contrast to the prison system guidance for those who have potentially come in contact with the virus but remain asymptomatic: They are allowed to use administrative “weather and safety” leave for up to 14 days.

“Everybody is saying, what the hell does this mean? If you have the symptoms? If you don’t have the symptoms?” said Rojas. “It’s just a mess.”

If conditions deteriorate to a lockdown or mass outbreak situation, “what happened in Italy could easily happen over here,” Rojas said.

McGlothin outlined the steps federal prisons would take as the threat grows: first canceling visitation, then limiting movement of prisoners transported between facilities, and finally locking down institutions. Lockdown conditions — in which inmates are kept in their cells except for limited showers — are not uncommon in individual federal prisons following violent events or even high levels of the flu, but they’re usually temporary.

It’s been more than 24 years since the entire federal Bureau of Prisons locked down. Inmates were fed in their rooms and all recreational activities were canceled following a series of prison riots in October 1995.

When asked about the possibility of a national lockdown, bureau spokesperson Emery Nelson declined to comment on the specifics of the contingency plans because of safety and security reasons.

Fifteen Democratic U.S. senators, including Elizabeth Warren and Bernie Sanders, sent a letter on Monday asking the Bureau of Prisons to explain its coronavirus plan. They had yet to get a response as of Thursday, according to Warren’s office.

David Patton, the executive director of the Federal Defenders of New York, a nonprofit that defends poor people accused of federal crimes, said he is concerned about the lack of information.

“I have no confidence that they’re prepared or whatever plans they have are acceptable from even the most minimal human rights perspective,” he said, stressing that a long-term lockdown would be unconstitutional because inmates need to have access to legal counsel.

Patton already had been sounding the alarm over inmate treatment at the federal Metropolitan Correctional Center in Manhattan following a recent lockdown. He detailed “hellish conditions” of inmates left in just boxer briefs in cold cells, a lack of access to soap, severe overcrowding and rodent infestations. And that’s without coronavirus added in.

“We’re starting with a baseline of mismanagement and poor conditions,” he said. “In the best of the times, we can’t get people medical care when they need it.”

Many advocates are pushing for officials to commute some inmates’ sentences to lessen the potential number of incarcerated individuals exposed to the virus. In San Francisco, public defender Mano Raju has pushed for the release of pretrial detainees who are older than 60 and have underlying medical conditions, as well as those up for work-release, electronic monitoring or with less than six months on their sentence.

Officials at every political level need to seriously consider such measures to protect the public, said Nazgol Ghandnoosh, a senior research analyst for The Sentencing Project, a group that pushes for criminal justice system improvements.

As does the public, Ghandnoosh noted. Even if people are not personally connected to anyone in prison, she said, they will be personally affected as inmates fill up hospital beds and ICU resources.