The Trump administration filed suit on Thursday against the city of Boston, Boston Mayor Michelle Wu, and the Boston Police Department, challenging an ordinance that restricts cooperation by the local police force with federal immigration officials.

The Trump administration’s complaint centers around the doctrine of preemption, which holds that federal law may displace state law if the state law frustrates a purpose or objective of a federal law or inappropriately encroaches on an area that has been specifically reserved for the federal government.

Immigration has consistently been deemed a province of the federal government. For instance, 8 US Code § 1373 states that no official may “prohibit, or in any way restrict, any government entity or official from sending to, or receiving from, the Immigration and Naturalization Service information regarding the citizenship or immigration status, lawful or unlawful, of any individual.”

The complaint alleges that the Boston Trust Act “is at cross-purposes with that congressional design,” specifically the portions that preclude local officials from “[p]roviding personal information … regarding a person’s release date or time to the federal Immigration and Customs Enforcement Agency … solely for the purpose of enforcing civil violations of United States immigration laws.”

A Department of Justice press release condemned Boston’s sanctuary policies—policies that tend to inhibit local law enforcement from cooperating with federal immigration enforcement. Attorney General Pamela Bondi said that “[i]f Boston won’t protect its citizens from illegal alien crime, this Department of Justice will.”

In response to Bondi’s letter “threatening to prosecute local officials” for failing to partake in “mass deportations,” Mayor Wu maintained that Boston’s actions are completely consistent with federal law:

The City of Boston follows the law—local, state, and federal. The United States Constitution establishes that local governments, closest to the people, hold the authority to enact public safety policies without the threat of unlawful interference from the federal government. The Founding Fathers included these protections as a direct result of the attempted coercion of Boston by an unaccountable and distant monarch, and this city’s refusal to bow down to tyranny.

The lawsuit is among a plethora of recent actions targeting sanctuary jurisdictions.