Federal immigration officers may deport immigrants to countries other than their own, with as little as six hours’ notice, even if officials have not provided any assurances that the new arrivals will be safe from persecution or torture, a top official said in a memo.

Todd M. Lyons, the acting director of U.S. Immigration and Customs Enforcement, wrote in a memo to the ICE workforce Wednesday that a Supreme Court ruling last month had cleared the way for officers to “immediately” start sending immigrants to “alternative” countries.

People being sent to countries where officials have not provided any “diplomatic assurances” that immigrants will be safe will be informed 24 hours in advance — and in “exigent” circumstances, just six. Those being flown to places that have offered those assurances could be deported with no advance notice.

If the State Department “believes those assurances to be credible,” then ICE may deport someone to that country “without the need for further procedures,” Lyons wrote in the memo, obtained by The Washington Post.

The United States has rarely deported people to countries where they are not citizens, and lawyers warned that thousands of longtime immigrants with work permits and families in the U.S. could now be uprooted and sent to places where they lack family ties or even a common language.

Among those who could be targeted are thousands of immigrants with final removal orders who have not been deported to their native countries because a judge found that they might face danger there. Others are those with deportation orders to countries such as China or Cuba that do not always cooperate with deportations because of their frosty relationship to the U.S.

Homeland Security Secretary Kristi L. Noem, whose agency oversees ICE, confirmed on “Fox News Sunday” that the agency had the policy in place. The memo is “incredibly important to make sure we get these worst of the worst out of our country,” she said.

“This is the same operation we had in the past, that people can go to third countries,” Noem said. “Many times, if other countries aren’t receiving their own citizens, other countries have agreed that they would take them in … and take care of them until their home country would receive them. That’s what this memo was confirming and that’s all been negotiated with that country through the State Department.”

Immigrants who state a fear of being deported will be screened for possible protection, Lyons wrote in the memo, but immigration lawyers said the government’s plan does not give immigrants enough time to assess the danger they might face in a country that the government has selected for them.

“It puts thousands of lives at risk of persecution and torture,” said Trina Realmuto, executive director of the National Immigration Litigation Alliance, which is challenging the third-country removals on behalf of immigrants in an ongoing federal lawsuit filed in Massachusetts.

The alliance filed the lawsuit in March arguing that the U.S. government was violating federal law and sending immigrants to places where they could be harmed or killed, without giving them a chance to argue against it, including a Guatemalan man deported to Mexico, where he had been kidnapped and raped.

U.S. District Judge Brian Murphy barred the government from removing immigrants without giving them a “meaningful” opportunity to challenge it. On June 23, the Supreme Court’s conservative majority paused the judge’s decision in a brief, unsigned statement that did not explain its reasoning, but it cleared the way for the removals to resume.

Justice Sonia Sotomayor, who wrote a stinging dissent with Justices Elena Kagan and Ketanji Brown Jackson, warned that the court’s decision would put people at risk. “In matters of life and death, it is best to proceed with caution,” she wrote. “In this case, the Government took the opposite approach.”

Since President Donald Trump took office promising mass deportations, officials have sent immigrants from Venezuela to a notorious mega prison in El Salvador, dispatched eight immigrants from Cuba, Vietnam, Myanmar, Laos, Sudan and Mexico to a conflict zone in South Sudan, and illegally deported a Salvadoran man, Kilmar Abrego García, to El Salvador even though an immigration judge’s order forbade it. The Trump administration brought Abrego back to the U.S. last month after the Supreme Court ordered them to facilitate his return, but in recent days government lawyers have said they could deport Abrego to a third country instead.

ICE and the Department of Homeland Security did not immediately respond to requests for comment about the memo on Saturday, or say how many immigrants are at risk of being deported.

Simon Sandoval-Moshenberg, the lead lawyer on a federal lawsuit in Maryland that successfully fought to return Abrego to the U.S., said the deportation procedures in the Lyons memo are “clearly inadequate” to prevent immigrants from being deported to countries where they might be at risk.

“It is definitely thousands upon thousands of people,” he said. “This is a category of people who understood themselves to be out of the woods.”

While in some cases immigrants could be deported to a country that has provided assurances that newcomers will be safe from torture or persecution, Lyons also outlines how officials should proceed if they are deporting people to a country that has not provided those guarantees.

In those cases, officers must follow a more limited procedure than the one Murphy had laid out in federal court in May after ICE attempted to deport immigrants to South Sudan. The judge said officers should screen the men to determine if they have a legitimate fear of removal, give them access to a lawyer and at least 10 days to challenge their removals. The Supreme Court ruling set aside that process, and the men were deported to South Sudan in recent days.

The Lyons memo says ICE can deport someone to a third country that has not offered any safety guarantees within 24 hours of notifying them where they are being sent. Officials will not ask immigrants if they fear being deported to that country, he wrote. Lyons’s memo is based on guidance Noem issued in a March memo, but provides additional details.

Immigrants who express a fear of being deported in the 24-hour period will be screened for possible humanitarian protection under federal law and the Convention Against Torture, which Congress ratified in 1994 to bar the government from sending immigrants to a country where they might face torture.

The screenings will “generally” occur within 24 hours to determine if migrants could merit immigration court proceedings, humanitarian protection, or if they should be deported to another alternate country.

However, Lyons wrote that “in exigent circumstances” immigration officers may deport someone as soon as six hours after notifying them of the third country.

In such cases, immigrants must be provided “reasonable means and opportunity to speak with an attorney” beforehand, he wrote, and the DHS general counsel or ICE’s top legal adviser must approve it.

Maegan Vazquez contributed to this report.