An unprecedented federal court ruling practically requires Department of Homeland Security officials to release criminal immigrants in many sanctuary cities, a pair of senators warned Monday.

A panel of Ninth Circuit Court Court of Appeals judges became the first circuit court in the country to rule that convicted criminal immigrants cannot be detained indefinitely while awaiting deportation proceedings unless Department of Homeland Security officials arrest them immediately upon their release from local custody — a near-impossible task to accomplish if local law enforcement officials won't cooperate with the DHS. The ruling is a break from other circuit courts, which ruled that the law allowing federal officials to detain criminal immigrants indefinitely applied even when the detention was delayed for some reason.

"[T]he Ninth Circuit has all but guaranteed that more dangerous criminal aliens in the nine states and several territories covered by its jurisdiction will be able to obtain a bond, be released from custody, and reoffend," Sen. Jeff Sessions, R-Ala., who chairs a Judiciary subcommittee on Immigration and The National Interest, said Monday. "Moreover, in sanctuary jurisdictions that refuse to hand over criminal aliens to DHS at all, much less immediately, the Ninth Circuit has guaranteed that dangerous criminal aliens will be able to roam free."

Violence committed by criminal immigrants who benefited from sanctuary city policies has received increased national attention this year. The shooting of Kate Steinle in San Francisco, Calif., for instance, and the death of Sarah Root, a Nebraska woman killed by an drunk driver, has prompted immigration hawks to introduce federal legislation cracking down on sanctuary cities. The Ninth Circuit ruling could exacerbate such problems, according to a Senate GOP aide, because it would allow many of the criminal immigrants who are currently priorities to be deported under President Obama's executive orders to be released on bond while they await their hearings before an immigration judge.

"The impact of this decision will be especially acute on immigration enforcement within the Ninth Circuit, which covers more sanctuary jurisdictions than any other circuit in the nation, including San Francisco, Los Angeles, Berkeley, Seattle, Portland, and dozens of others," Sessions and Senate Judiciary Committee chairman Chuck Grassley, R-Iowa, wrote in a letter to Attorney General Loretta Lynch. "These sanctuary jurisdictions refuse to hand over criminal aliens to DHS at all, much less immediately, meaning that the Ninth Circuit's decision will prevent DHS from guaranteeing the detention of the most dangerous criminal aliens in those jurisdictions."

Grassley and Sessions want Lynch to ask for the Ninth Circuit court to reconsider the panel's decision; failing that, they asked Justice Department to fight the ruling at the Supreme Court.

"It is a clear and unavoidable duty of the Department of Justice to defend vigorously the lawful statutes passed by Congress, and to have them interpreted as intended," the senators wrote.

The Justice Department has adopted the Judiciary Committee lawmakers' position in an analogous case earlier this year.

"[A] criminal alien does not become exempt from mandatory detention under Section 1226(c) merely because there is a gap in time between his release from criminal custody and the onset of his immigration custody," Solicitor General Donald Verrilli and other DOJ lawyers wrote in a May filing before the Supreme Court.

The case could present a rare moment of agreement between Senate Republicans and the Obama administration, who regularly clash over immigration enforcement policy. "It goes right to the heart of what it is that they claim they want to do, and that's go after criminals," a Senate GOP aide told the Washington Examiner. "The government actually, for the most part, wants to be able to protect [this law] because if they lose that it's going to open the floodgates to a lot more criminals on the streets and that's not going to be what they want."