U.S. Immigration and Customs Enforcement is moving 1,600 detainees into federal prisons to address overflows from the surging number of prosecutions resulting from the Trump administration’s new “zero-tolerance” policies, the agency said Thursday.

The arrestees, who face deportation and are awaiting civil immigration hearings, will be routed to prisons in Washington, Texas, Oregon, Arizona and California, where the United States Penitentiary in Victorville outside of Los Angeles will receive 1,000 of them.

“Due to the current surge in illegal border crossings and implementation of the U.S. Department of Justice’s zero-tolerance policy, U.S. Immigration and Customs Enforcement is working to meet the demand for additional immigration detention space,” spokeswoman Danielle Bennett said in a statement.

Bennett said the use of the federal facilities is intended to be temporary, until ICE can contract out new detention facilities or until the surge of illegal border crossings subsides.

The number of arrests made by U.S. border agents has risen to more than 50,000 for each of the past three months, the highest levels since illegal immigration numbers dipped after Trump took office. The Department of Homeland Security took 52,000 migrants into custody in May — nearly three times the number from the same month in 2017. The reversal has angered the president and left him furious at Homeland Security Secretary Kirstjen Nielsen and other aides.

Michael Kaufman, a senior staff attorney at the American Civil Liberties Union of Southern California, said the news was a disturbing development. Until now, he said, civil detainees had been held by ICE in county jails or by contract in privately run facilities.

“What’s different about this is, this is the first time we’ve seen ICE putting people in an actual prison as opposed to jail or a privately run facility, and that’s why it gives lie to the notion that immigration detention is civil,” he told The Washington Post. “Civil detainees should be held in conditions that are appropriate for somebody who is merely being held for non-punitive reasons. And if they’re being placed in facilities that were built to hold people who have been convicted of crimes and who are being punished, that raises really serious concerns.”

Leaders of prison unions in some of the affected states told Reuters, which first reported the story, that they did not have much time to prepare for the influx.

John Kostelnik, local president for the American Federation of Government Employees Council of Prison Locals union, told the news service that workers were moving inmates around to try to make space.

“There is so much movement going on,” Kostelnik said. “Everyone is running around like a chicken without their head.”

The number of arrests and ensuing detentions follows a tightening of the Trump administration’s hard-line immigration policies. Attorney General Jeff Sessions recently announced the “zero tolerance” policy, threatening anyone caught crossing the border illegally with federal criminal charges.

That has significantly increased the number children being separated from their parents, which has become an emotional flash point in the national debate over immigration.

Kaufman said he saw similarities in the transfer of detainees to other punitive immigration measures, like the child separations.

“They are trying to punish people for lawfully going through the immigration process,” he said. “They’re saying they’re going to keep more and more people locked up, even if there isn’t a reason to do so, while they go through the immigration process.”

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