A federal appeals court serving New England has been asked to decide whether thousands of detained immigrants have the right to bond hearings.

On Monday, a panel of judges from the 1st U.S. Circuit Court of Appeals heard arguments in a lawsuit alleging the federal government is illegally holding immigrants without giving them an opportunity to advocate for their release before an immigration judge.

A U.S. District Court judge in Boston sided with the plaintiffs — civil rights groups, including the American Civil Liberties Union of Maine, which sued the Department of Justice and the Department of Homeland Security last year. The government appealed.

Despite the Boston judge’s ruling, and a similar one by a federal judge in California last fall, immigration judges have continued to deny bond hearings to immigrants in federal detention. Immigration judges are overseen administratively by the DOJ.

Appeals Court Judge Sandra Lynch asked John Bailey, an attorney for the government, on Monday whether that would continue, should the court rule against them.

Bailey said he wasn’t aware of the government’s position on that, but that they consider bond hearings “purely a creature of implementation,” as opposed to a legal right.

Bailey argued that Congress passed a reform act in 1996 “to end differential and more favorable treatment to aliens who successfully invade our border and make it to the interior of our country.” He argued that federal law allows for the mandatory detention of anyone who enters the country without inspection.

Plaintiffs have argued that the law is not so clear cut, and that the Trump administration’s current practices contradict decades of precedent in which immigrants who have been living in the country without legal status, and do not have criminal histories, have been spared detention and granted bond hearings.

The two sides disagreed on the intentions of Congress when it passed immigration reform laws, including whether lawmakers intended for widespread detention, and what it means for an immigrant to be “seeking admission” to the United States versus “applying” for admission.

There is no deadline for the appeals court’s decision.