A recent order from a federal district court judge in Baltimore may slow President Donald Trump’s aggressive deportation agenda in Maryland.

The May 21 ruling from Chief District Judge George L. Russell III temporarily prohibits the federal government from deporting someone or altering their immigration status if they challenge the legality of their arrest by filing a writ of habeas corpus in federal court.

Habeas corpus, a person’s right to challenge their incarceration before a judge, is one of the foundational tenets of the U.S. legal system but a relatively uncommon matter in immigration proceedings aside from cases of prolonged detention.

Now immigration attorneys are using the bedrock legal principle as a kind of last resort to help keep their clients in the country amid the Trump administration’s effort to speed deportations.

A writ of habeas is a challenge to an individual’s detention, not whether they can be removed from the United States, which is a matter for an immigration judge to determine. But the two issues are closely linked, said Austin Rose, managing attorney at the Amica Center for Immigrant Rights.

Russell’s standing order will allow the court time to review the grounds of an individual’s arrest before Immigration and Customs Enforcement can unilaterally remove them from the country, he said. A representative from the U.S. District Court of Maryland declined to provide additional comment on the order.

“This makes it easier to constrain illegal actions,” Rose said, because it will temporarily prevent ICE from deporting someone before they have had a chance to challenge the underlying arrest in federal court.

The May 21 order applies to all who file for habeas in Maryland but is temporary. It prevents removal for two business days, and during that time the court could decide to extend it on a case-by-case basis.

That difference of days is critical because it becomes harder to challenge arrest and deportation if someone has already been removed from the country, said Elizabeth Keyes, professor of law at the University of Baltimore.

“Habeas slows the machinery down,” Keyes said.

A representative from the U.S. Department of Justice declined to comment on the order. The Department of Homeland Security and ICE did not respond immediately to a request for comment.

In Washington, habeas corpus has become a political hot-button issue, with accusations that leading Trump administration officials don’t understand what it means or believe the right should be suspended.

When asked to define habeas corpus during a May hearing before the U.S. Senate, U.S. Secretary of Homeland Security Kristi Noem said in part that it is “a constitutional right the president has to be able to remove people from this country.” She was continuing her answer when cut off by Sen. Maggie Hassan, a New Hampshire Democrat, who said her definition was incorrect.

Presidential adviser Stephen Miller has also floated the possibility of suspending habeas, an action historically taken only during times of war.

Noem’s department, which oversees ICE, has spent the first months of the second Trump administration pushing legal boundaries and, in some cases, violating the law, legal experts say.

In April, a federal judge called the deportation of Kilmar Abrego Garcia, a Salvadoran immigrant who had been residing under a protected legal status in Maryland, “wholly lawless” and questioned the underlying legality of his arrest. ICE removed Abrego Garcia from the U.S. just three days after his arrest.

ICE deported him alongside hundreds of Venezuelans quickly removed under the Alien Enemies Act. Many of them were also residing lawfully in the country and did not have criminal histories, according to media and human rights reports. (A federal judge ruled on Wednesday that the Trump administration must give more than 100 migrants sent to a notorious prison in El Salvador a chance to challenge their deportations.)

The standing habeas order could have prevented those removals, Keyes said.

“The government has so much latitude in immigration, but it’s not a Constitution-free zone,” Keyes said. “They [immigrants] are entitled to due process even in the Wild West of immigration court.”

Robert Koulish, a research professor and director of the undergraduate law programs at the University of Maryland, believes the order will perhaps deter future “middle of the night” deportations to El Salvador, South Sudan or elsewhere.

Baltimore City Council member Mark Parker, who has raised concerns about the Trump administration’s approach to immigration enforcement in Maryland, said the latest ruling is “a welcome development,” but it does not “provide any immigration relief” and “doesn’t help anyone gain a new legal status that they don’t already have.”

“This seems to only delay a deportation for certain individuals, or at least prevent certain individuals from being deported from the U.S. to a different country,” he said.

The Trump administration has further expanded the list of who it deports without an appearance before an immigration judge. Those at risk of an expedited removal are immigrants in the country for less than two years, including those who entered the country lawfully under the expanded use of “humanitarian parole” for asylum seekers.

“It’s very clear that ICE is detaining people without a plan for what to do with them,” said Rose, whose organization has sued ICE over the conditions inside its Baltimore holding room.

Last month, a federal judge ordered ICE not to deport two women who lawyers say had been residing in the country lawfully and spent days in cells designed to hold people for hours at a time.