On Tuesday, Department of Homeland Security Secretary Kirstjen Nielsen told the Senate Judiciary Committee that she would be asking the Department of Justice to look into prosecuting officials in sanctuary cities. “The Department of Justice is reviewing what avenues may be available,” she said. President Trump has already threatened to withhold funding from sanctuary cities.

This strategy could actually bear legal fruit, according to Jessica Vaughan of the Center for Immigration Studies. She told The Daily Caller that, “a criminal case against a sanctuary official or government is possible, although probably as a last resort, after they have exhausted other options, and when the facts of the case are particularly egregious or concerning.” The governing statutes are typically used to prosecute human traffickers who hide illegal immigrants from federal detention; that law could theoretically be applied against local officials who refuse to detain illegal immigrants after a request from the federal government.

This argument is legally dicey, since the legal counterargument would be that the federal government cannot use the states as their law enforcement agencies. As Professor Erwin Chermerinsky, dean of the University of California at Berkeley School of Law, writes:

Under the anti-commandeering principle, the federal government can no more require state and local governments to help it carry out mass deportations than it can require local officers to investigate and enforce federal gun laws.

With that said, Nielsen’s comments will likely touch off a firestorm — and could lead to conflict between federalists among conservatives and immigration hawks.