In oral arguments Wednesday, the U.S. Supreme Court appeared evenly split over a case out of California that sets some limits on long-term detention of immigrants.

The case, Jennings v. Rodriguez, deals with the rights of legal permanent residents who are subject to deportation because they've been convicted of crimes, and asylum seekers who have met the government's initial criteria for protection from persecution. Both groups are subject to mandatory detention while they fight deportation in immigration court.

There are roughly 8,000 such detainees on any given day. They are among more than 400,000 immigrants detained by the Department of Homeland Security in the course of a year. Those numbers could increase if President-elect Donald Trump makes good on his pledge to deport millions of unauthorized immigrants and immigrants with criminal histories.

In 2015 the U.S. Court of Appeals for the Ninth Circuit, in San Francisco, upheld a lower court ruling that said that these detainees are entitled to hearing before an immigration judge every six months to consider them for release while their immigration cases proceed.

Ahilan Arulanantham, an attorney for the American Civil Liberties Union, is representing the immigrants. He told the Supreme Court justices that some of his clients have spent years behind bars. He urged the justices to affirm that a bond hearing to consider release is a right under the Constitution's due process clause.

“That's all we are talking about, just the minimal requirement of a hearing in front of a neutral decision maker for people who have had very, very long periods of incarceration," Arulanantham said.

But U.S. Solicitor General Ian Gershengorn challenged the notion that the length of incarceration has any bearing on the constitutionality of detention, as long as the government is making reasonable progress at resolving a person’s immigration status.

Justice Sonia Sotomayor asked the solicitor general what standard a court would apply to determine whether a person’s detention was unconstitutional.

Gershengorn said the court should ask: "Has there been some sort of unusual situation or misconduct on the part of the government, or delay on the part of the government, that suggests the purpose of detention was not to effectuate removal?"

Gershengorn said that immigrants who challenge their deportation may wind up detained for long stretches because the immigration system offers them a robust system of appeals, and those appeals take time.

He told the justices that 90 percent of hearings before an immigration judge occur within 14 months, and 90 percent of immigration appeals proceedings are done within 19 months.

That prompted Sotomayor to respond: "We are in an upended world when we think 14 months or 19 months is a reasonable time to detain a person."

The Ninth Circuit held that immigrants must be released on bond unless the government can prove that they are a danger to public safety or a flight risk. Some of the justices took issue with that approach.

Chief Justice John Roberts noted that the appeals court's decision shifts the burden off of the immigrant to provide proof that they are not a danger or a flight risk.

"Our job is to read the statute" Roberts quipped. "But we can't just write a different statute."

Justice Samuel Alito suggested, “We could simply say the Ninth Circuit's interpretation of the statute is wrong and remand [it back to the lower court] for further proceeding.”

Speaking outside the courthouse after the hearing, the ACLU’s Arulanantham said that the ruling the eight justices reach could have a profound effect on thousands of immigrants in California and the other Western states in the Ninth Circuit.

"There are thousands of people who have been released under these bond hearings,” he said, “who’ve returned to their families, who are out of prison, basically who are living their lives" while their cases proceed through immigration court.

Arulanantham said a reversal of the Ninth Circuit’s decision could allow the government to round those people up again.

The Supreme Court must rule on the Jennings v. Rodriguez by June, 2017.