DENVER — On Friday, the Department of Justice sued Colorado and Denver for allegedly getting in the way of government efforts to enforce immigration laws. This is the latest move by the Trump administration to go after what some people call “sanctuary cities” and policies.

The lawsuit says that the state and its largest city, Denver, have passed “sanctuary laws” that are against the U.S. Constitution’s Supremacy Clause.

It says that the US has “well-established, preeminent, and preemptive authority to regulate immigration matters.” The lawsuit was filed in federal court in Denver.

There isn’t a clear definition of sanctuary laws or cities, but in general, they mean that local governments don’t work with Immigration and Customs Enforcement as much as they could. ICE is in charge of enforcing U.S. immigration laws all over the country, but they need help from the states and local governments, especially when they have to remove a lot of people. They ask that police and sheriffs tell ICE about people they want to deport and hold them until federal officers arrive.

The Department of Justice has sued Chicago and Rochester, New York, for the same thing.

Lawyers for the Justice Department say that Colorado’s “sanctuary policies” let the Venezuelan gang Tren de Aragua take over an apartment complex in Aurora, a suburb of Denver.

Trump said that the gang had taken over big parts of the city, but local officials said that was not true. They did say that the apartment complex was terrorized by people with ties to Tren de Aragua.

Democratic Gov. Jared Polis, the state Legislature, Denver Mayor Mike Johnston, and Colorado Attorney General Phil Weiser are all named as defendants in the case filed on Friday.

In an email, Polis’s spokesman, Conor Cahill, said that Colorado is not a sanctuary state and that it works with local, state, and federal police all the time.

“We will follow the court’s decision if they say that any Colorado law is not valid,” he said. “We are not going to say anything about the lawsuit’s validity.”

Republicans in Congress have put pressure on city leaders who are Democrats to support the Trump administration’s immigration plan. Last month, the mayors of Denver, Boston, New York, and Chicago were asked to appear before the House Committee on Oversight and Government Reform.

The mayors fought back, saying that their cities were safe and welcome places and not lawless danger zones. They also asked Congress to pass immigration reform.