The Trump administration has filed a federal lawsuit against the city of Boston and its leaders, marking the latest move in its campaign to dismantle sanctuary city policies across the country.

The lawsuit was filed Thursday in U.S. District Court for the District of Massachusetts, NBC 10 reported.

It targets the Boston Trust Act, a local ordinance that limits how the Boston Police Department interacts with federal immigration enforcement.

Under the law, city police are instructed to cooperate with U.S. Immigration and Customs Enforcement only in matters that involve public safety.

Police are directed not to participate in civil immigration enforcement, including detaining people at ICE’s request unless there is a criminal warrant.

The Justice Department argues the law violates the Supremacy Clause of the U.S. Constitution, which establishes that federal law takes precedence over conflicting state or local laws.

In its complaint, the department alleged that Boston’s sanctuary policies have resulted in the release of dangerous criminal aliens who should have been transferred to ICE custody.

Attorney General Pamela Bondi sharply criticized the city’s approach.

“The City of Boston and its Mayor have been among the worst sanctuary offenders in America — they explicitly enforce policies designed to undermine law enforcement and protect illegal aliens from justice,” Bondi said. “If Boston won’t protect its citizens from illegal alien crime, this Department of Justice will.”

“Not only are Boston’s sanctuary city policies illegal under federal law, but, as alleged in the complaint, Boston’s refusal to cooperate with federal immigration authorities results in the release of dangerous criminals from police custody who would otherwise be subject to removal, including illegal aliens convicted of aggravated assault, burglary, and drug and human trafficking, onto the streets,” The Department of Justice press release said.

“On her first day in office, Attorney General Bondi instructed the Department’s Civil Division to identify state and local laws, policies, and practices that facilitate violations of federal immigration laws or impede lawful federal immigration operations. On Aug. 5, Attorney General Bondi published a list of sanctuary jurisdictions, which included the City of Boston, and vowed to bring litigation to end these policies nationwide. Today’s lawsuit is the latest in a series of lawsuits brought by the Civil Division targeting illegal sanctuary city policies across the country, including in New York, New Jersey, and Los Angeles, California,” it said.

Boston Mayor Michelle Wu, who was named as a defendant alongside Boston Police Commissioner Michael Cox, defended the ordinance.

“This is our city and we will vigorously defend our laws and the constitutional rights of cities, which have been repeatedly upheld in courts across the country,” Wu said. “We will not yield.”

Wu added that Boston remains “a thriving community, the economic and cultural hub of New England, and the safest major city in the country.”

“But this administration is intent on attacking our community to advance their own authoritarian agenda,” she said.

Constitutional experts say the case faces steep challenges.

“I think there is no case law, precedent, or anything to support the federal government forcing a state government to do federal duties,” attorney Joseph Malouf told NBC10 Boston.

There is no legal definition of a sanctuary city. The term is generally used to describe jurisdictions that place limits on their cooperation with ICE detainer requests and federal immigration enforcement.

Supporters say such policies strengthen trust between police and immigrant communities, while opponents argue they allow criminals to remain free rather than being deported.

The Trump administration has made rolling back sanctuary policies a priority.

It has filed similar lawsuits against Los Angeles, New York City, Denver, Rochester, New York, and four New Jersey cities earlier this year.

The Boston lawsuit signals that the White House intends to keep pressing the issue ahead of the 2026 midterm elections.