Immigrant advocates marched from Philadelphia’s Independence Hall to the federal courthouse to show support for a New Jersey law against privately-run immigration detention centers. It’s an especially volatile issue, since the Trump administration ramped up arrests and deportations sweeping up thousands, but desperate for space to lock them up.

“They’re disappearing immigrants in our communities — and we are here to make sure that NJ does not become a detention state.”

“For every person stripped of dignity — for every child who misses a parent — we say, no more! No more! No more!”

While protesters rallied on the street, lawyers upstairs argued before a Third Circuit panel of appellate judges. Their focus: the Elizabeth Detention Center, run by CoreCivic under a federal contract with U.S. Immigration and Customs Enforcement. Gov. Phil Murphy did sign a law barring the feds from hiring private firms to run immigrant detention facilities, but a lower court judge struck that down. Thursday, New Jersey and a long list of good government allies defended the state law against charges that it violates the Constitution’s Supremacy Clause — which gives federal law primacy over state statutes.

“They’re not saying that the state is trying to regulate the federal government. What they’re saying is that the state can take action to protect the state from horrific conditions that exist in private immigration detention centers ,” explained ACLU-NJ Staff Attorney Molly Linhorst.

The law would still allow ICE to lease, build or buy its own lock-up , insisted the state’s attorney Jeremy Feigenbaum, adding, “There’s no way ICE couldn’t run the Elizabeth Detention Center itself.”

CoreCivic’s attorney Bradley Simon argued, “This is an interference with the federal government’s right to do their business…a major road block in their right to do their job, with catastrophic effects.” He said, the 300-bed Elizabeth facility is New Jersey’s only remaining immigrant detention center. Citing its proximity to Newark and John F. Kennedy International Airports, Simon said closing it would force ICE to relocate detainees hundreds of miles away from their families and attorneys. But another company — GEO Group — is moving to open Delaney Hall, a 1000-bed immigrant detention facility in Newark, under a new contract it signed with ICE. So there’s a lot at stake for the immigrant community.

Legal arguments ran over two hours, as the three-judge panel pressed attorneys with questions. McKaye Neumeister, attorney for the U.S. Department of Justice, accused New Jersey of “trying to prohibit ICE from working with the contractor to carry out federal operations.”

But the judges wondered whether a clear federal law could better solve the conflict . Judge Thomas Ambro asked, “Isn’t the easiest thing to get Congress to draft something that supports your position — hook, line and sinker?”

“I think it was a really robust argument. And clearly these are really fundamental questions they’re dealing with— relating to what states and the federal government can do. So there’s gonna be a lot that they’re gonna have to think through,” Linhorst said.

The court reserved decision which won’t just affect New Jersey — other states are watching this case closely.