The Oregon Supreme Court announced a new rule last week that bars Immigration and Customs Enforcement (ICE) agents from arresting undocumented people in state courthouses without an arrest warrant.

The Trump administration isn’t happy about it.

Oregon Chief Justice Martha Walters announced the new rule on November 14, saying in a statement that it would “protect the integrity of the state judicial process, and will allow state courts to fully hold accountable people accused of a crime.” The new guideline is now part of Oregon’s Uniform Trial Court Rules, a list of policies which apply to circuit courts in each of the state’s 36 counties.

“Arrests in courthouses have interfered with judicial proceedings and removed criminal defendants before they have been sentenced or completed their sentences,” Walters added. “We are adopting this rule to maintain the integrity of our courts and provide access to justice—not to advance or oppose any political or policy agenda.”

A week later, and US Attorney General William Barr is calling on Walters to reverse the rule. In an open letter sent Thursday, Barr asked Walters to “reconsider this dangerous and unlawful course of action.”

The letter is addressed to both Walters and Washington Supreme Court Chief Justice Mary, who is considering a similar rule for Washington state. Washington and Oregon are both sanctuary states, meaning local law enforcement does not go out of its way to assist with federal immigration agents.

Barr’s argument, in a nutshell: Denying undocumented people due process procedure puts Americans at risk.

“Instead of permitting the safe transfer of custody of criminal aliens in a secure environment,” Barr wrote, “these dangerous state laws and policies force federal law enforcement officers to locate and arrest criminal aliens at-large within communities at potentially great peril to the officers and the public.”

Barr went so far as to include a list of particularly egregious crimes committed by undocumented people living in sanctuary states, claiming these isolated instances prove that sanctuary policies have “endangered the lives of the citizens of your states.” But Barr’s logic doesn’t quite hold up under scrutiny: As a recent analysis from the libertarian think-tank Cato Institute concluded, undocumented immigrants “are less likely to be criminals than native-born Americans.”

After announcing the rule last week, Walter received praise from different immigration advocacy groups, including Causa Oregon, Adelante Mujeres, and the ACLU of Oregon. These groups had raised concerns about an increase of ICE arrests at courthouses during the Trump presidency, and had urged the Oregon Supreme Court to ban the practice.

“We hear too often from devastated family members whose loved ones have been snatched up out of Oregon courthouses by people in street clothes and stuffed into unmarked cars and driven off,” said Cristina Marquez, interim executive director of Causa Oregon, in a press release issued after Walters announced the new rule. “People have been afraid to go to the courthouses.”

Carl McPherson, executive director of Metropolitan Public Defenders—the largest public defense firm in the state—said the new rule meant that “our clients, witnesses, and other court-goers can participate in our judicial system without fear of being arrested and detained by ICE.”

It’s not clear what impact—if any—Barr’s letter will have on the new Oregon rule. Oregon has established itself in recent years as a state willing to stand up to the Trump administration, particularly on issues of immigration and criminal justice. The new rule also has the support of Oregon Attorney General Ellen Rosenblum, meaning she’d likely defend it in the event of a legal challenge.