The Trump administration sued the city of Boston and its leaders Thursday in its latest attempt to invalidate policies seen as interfering with immigration enforcement.

The suit alleges that Boston’s sanctuary city policies are illegal under federal law and the city’s refusal to cooperate with immigration authorities has resulted in the release of dangerous criminals who should be deported.

“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,” Attorney General Pamela Bondi said in a statement. “If Boston won’t protect its citizens from illegal alien crime, this Department of Justice will.”

The administration has filed a series of similar lawsuits against other cities, including Los Angeles, New York City, Denver and Rochester, New York. It sued four New Jersey cities in May.

Boston Mayor Michelle Wu, who was named as a plaintiff in the latest lawsuit, said in a statement Thursday that Boston will “vigorously defend our laws and the constitutional rights of cities.”

“This unconstitutional attack on our city is not a surprise,” Wu said. “Boston is 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.”

There is no strict definition for sanctuary cities, but the terms generally describes places that limit cooperation with Immigration and Customs Enforcement. ICE enforces immigration laws nationwide but seeks help from state and local authorities to identify immigrants wanted for deportation and hold them for federal officers.