The Trump administration is reportedly sending armed and highly trained law enforcement units to sanctuary cities across the country to support US Immigration and Customs Enforcement in carrying out immigration raids.

As first reported by the New York Times, 100 US Customs and Border Protection officers, including those from the SWAT-like Border Patrol Tactical Unit, will be deployed from February through May across nine sanctuary cities: Chicago, New York, San Francisco, Los Angeles, Atlanta, Houston, Boston, New Orleans, and Newark, NJ.

Border Patrol Tactical Unit agents receive special training for high-risk law enforcement activities, including sniper certification and other advanced weapons training. Their primary charge has been tracking down drug traffickers on the US-Mexico border, where violence can often break out, but now they will also be responsible for conducting routine immigration arrests in some of America’s largest cities, according to the Times.

It’s just the latest instance in which President Donald Trump has sought to target sanctuary cities — which do not allow local law enforcement to share information with ICE or hand over immigrants in their custody — for refusing to cooperate with federal immigration authorities. Immigrants advocates say that the deployment is not only a waste of federal law enforcement resources, it also might endanger immigrant communities.

“This is transparent retaliation against local governments for refusing to do the administration’s bidding,” Naureen Shah, senior policy and advocacy counsel on immigrants’ rights for the American Civil Liberties Union, said in a statement. “It will put lives at risk by further militarizing our streets.”

Department of Homeland Security spokesperson Heather Swift said in a statement Friday that the additional CBP agents (which she emphasized come from a variety backgrounds and not just tactical units) will help overstretched ICE officers deal with the rising number of immigrants who could be arrested on immigration violations but have yet to be detained.

“ICE does not have sufficient resources to effectively manage the sustained increase in non-detained cases which is exacerbated by the rise of sanctuary jurisdictions,” she said. “These officers have also been trained in routine immigration enforcement actions, which is what they have been asked to do.”

It’s all part of Trump’s campaign against sanctuary cities

Friday’s decision is just one in a long line of Trump’s attempts to crack down on sanctuary cities. The administration has tried to withhold federal law enforcement grants from sanctuary states and vacate California’s sanctuary laws (but has mostly failed). And it recently blocked New Yorkers from enrolling in Global Entry and other programs that offer faster processing for pre-vetted travelers in response to new state sanctuary laws.

At his State of the Union address earlier this month, Trump characterized sanctuary cities as a danger to public safety and broadly painted immigrants as violent criminals, highlighting a case of an immigrant arrested on charges of murdering and sexually assaulting a 92-year-old woman in New York City.

Trump has done this over and over during his time in office, turning his ire on international criminal gangs like MS-13 and invoking the stories of “angel moms,” parents of those killed by gang members.

But in reality, research suggests that his characterization doesn’t hold water: Sanctuary policies don’t appear to make a city more dangerous. While there isn’t a huge body of research on sanctuary policies’ impact on crime rates, studies have found that they either slightly decrease crime rates or have no effect.

A study published in the journal Urban Affairs Review in 2017 found that cities with similar characteristics but for their sanctuary policies had “no statistically discernible difference” in their rates of violent crime, rape, or property crime. Using data from the National Immigration Law Center and the FBI, researchers compared crime rates before and after cities passed sanctuary laws, finding that they had no effect on crime.

Another study by the Center for American Progress, a left-leaning think tank, examined the almost 2,500 counties that don’t accept requests from US Immigration and Customs Enforcement to detain unauthorized immigrants. The study found that counties with sanctuary policies tend to have lower crime rates than those that don’t: about 35.5 fewer crimes per 10,000 people on average. The counties with the smallest populations exhibited even bigger differences in crime rates.

Many police chiefs say there’s good reason behind those results: Sanctuary policies facilitate better crime reporting and cooperation with law enforcement in criminal investigations.