Over 3,000 medical professionals are demanding the immediate release of all detainees held in immigration facilities by ICE, warning of deadly consequences as COVID-19 continues to spread.

In an open letter sent to the US immigration agency this week, medical workers point out that the conditions of overcrowded prisons, jails, and detention facilities guarantee the rapid spread of sickness and disease—including the highly-contagious and life-threatening virus that has paralyzed cities across the world.

“Considering the extreme risk presented by these conditions in light of the global COVID-19 epidemic, it is impossible to ensure that detainees will be in a ‘safe, secure and humane environment,’ as ICE’s own National Detention Standards state,” the letter reads. “As such, we strongly recommend that ICE implement community-based alternatives to detention to alleviate the mass overcrowding in detention facilities.”

The letter is being spearheaded by Doctors for Camp Closure and New York Lawyers for the Public Interest (NYLPI), which works with incarcerated populations. As of Wednesday, the letter has been signed by more than 3,000 doctors, nurses, and medical professionals.

Medical experts warn that this not only needlessly endangers the lives of tens of thousands of immigrants and asylum seekers—many of whom have never been charged with a crime—but threatens to infect prison staff and the surrounding communities, further straining emergency medical resources.

“What happens in there happens in the community as well,” Nathaniel Kratz, an instructor of medicine at Columbia University’s Irving Medical Center and a member of NYLPI’s medical steering committee, told Motherboard. “The conditions and the outbreaks that happen in these facilities are going to be reflected in the communities of which they’re a part.”

The letter comes as pressure builds on officials to take drastic measures to slow the spread of COVID-19, which the World Health Organization has declared a global pandemic.

This weekend, courts in Ohio began releasing hundreds of inmates in an effort to contain the virus. Brooklyn District Attorney Eric Gonzalez similarly announced Tuesday that his office would “immediately decline to prosecute low-level offenses that don’t jeopardize public safety,” as a measure to stem the flow of people into New York City’s overcrowded prison system. And in Iran, where 129 fatalities were recently reported in a single day, the government has released 85,000 prisoners to fight back the disease.

Despite the pandemic, US immigration agencies are showing no signs of deviating from business as usual. Even after Mayor London Breed announced a “shelter-in-place” order in San Francisco, ICE agents donned masks and continued to raid and arrest immigrants in the city. Speaking to Mother Jones, one Cuban asylum seeker detained at a for-profit jail in Louisiana said that “it’s going to be a massacre” once the coronavirus inevitably arrives at the overcrowded facility.

“The idea that we continue to place people into the detention and deportation machine right now when we can’t assure the health of the people who are already in the system is really appalling,” Marinda van Dalen, a senior staff attorney at NYLPI, told Motherboard.

Even absent a full-blown pandemic, disease and illness regularly rips through jails and prisons, where overcrowded inmates live in unsanitary conditions with artificially scarce access to basic hygiene products like soap and toilet paper.

“Based on our experience working with people who are in immigration detention in New York, we’ve seen these facilities are unable to provide even basic medical care to people,” said van Dalen. “Over and over we’ve seen that the care that they’re receiving is inadequate, and that’s when we’re not facing the kind of health crisis that’s now upon us.”

An ICE spokesperson did not respond to Motherboard’s request for comment.

“These are spaces that are created for control, they are not spaces created for hygiene,” said Kratz. “All of the basic public health measures that we use to prevent the spread of infectious disease are either severely lacking or absent.”

Even when treatment is available, prisons and jails have historically failed to provide it to those locked inside. For example, Kratz pointed out that during the H1N1 outbreak in 2009, less than half of the country’s incarcerated population was given the vaccine. And in Michigan, nearly half the state’s prisons are currently locked down after experiencing a flu outbreak exacerbated by conditions inside, he said.

Last year, at least 3 children died of the flu after US immigration agencies refused to vaccinate the tens thousands of people held in their detention facilities. In December, Doctors For Camp Closure responded by setting up a mobile clinic to vaccinate children being held at a CBP detention facility outside San Diego. But the doctors were turned away—and one charged with a misdemeanor—after attempting to provide the inoculations.

Given COVID-19’s rapid spread—and the current lack of a vaccine—activists across the country are demanding authorities release inmates and detainees as the only moral course of action. On Monday, the ACLU filed a lawsuit against an ICE detention facility in Seattle, demanding the agency immediately release individuals who are at high risk of illness or death from the virus.