U.S. Immigration and Customs Enforcement has thus become more prevalent, leaving local communities to search for a balance between addressing federal regulation and keeping their locality safe. States, however, have no obligation to enforce federal immigration laws—and studies have shown that doing so may actually threaten the trust that holds their communities together.

This battle between immigrant-friendly cities and federal immigration enforcement came to the forefront this month as two Massachusetts district attorneys, along with public defenders and community groups, brought suit against ICE over courthouse arrests.

ICE policy prevents its officers from taking enforcement actions in schools, medical treatment centers, or places of worship, as well as during events like funerals, weddings, or public demonstrations. Courthouses, however, provide ICE the opportunity to plan arrests of undocumented immigrants who may be scheduled to appear for a case unrelated to their status.

The department reported arresting nearly 160,000 undocumented immigrants in 2018, an 11% increase from the year prior. Although this data includes all locations of arrest, a January 2018 policy enshrining ICE officers’ right to make arrests within courthouses likely aided in the boost. The Immigrant Defense Project reported that in New York state alone, ICE operations around courthouses increased 1,700% between 2016 and 2018.

A report on courthouse immigration arrests published by the American Civil Liberties Union in 2018 states these increases “have sown confusion and spread fear and mistrust—limiting the efficacy of the judiciary, law enforcement, survivors’ services, public defenders, and other core services available at courthouses.”

The chief justices of California, New Jersey, and Seattle have each individually requested ICE cease enforcement actions at courthouses in recent years, all citing the chilling effect the practice has on the community.

The Massachusetts complaint against ICE alleges that the department’s civil courthouse arrest policy “is undermining the work of both prosecutors and defense attorneys by deterring many victims and witnesses from appearing in court, forcing the District Attorneys to abandon otherwise promising prosecutions.”

According to the lawsuit, ICE’s courthouse arrests are illegal for three reasons. First, the Supreme Court has established that “common-law privilege against civil courthouse arrests is ‘well settled.'” Second, the practice allegedly violates the Tenth Amendment by exceeding federal powers in state court. Finally, the complaint argues that the practice “violates the Constitutional right of access to the courts, which prohibits ‘systemic official action [that] frustrates a plaintiff or plaintiff class in preparing and filing suits.'”

ICE’s policy on courthouse arrests argues that the practice is “wholly consistent with longstanding law enforcement practices, nationwide.”

“The arrest of persons in a public place based upon probable cause is legally permissible,” reads the ICE website. “ICE officers and agents are expressly authorized by statute to make arrests of aliens where probable cause exists to believe that such aliens are removable from the United States.”

Moreover, the department states these arrests are “often necessitated by the unwillingness of jurisdictions to cooperate with ICE in the transfer of custody of aliens from their prisons and jails.”

This “unwillingness” likely refers to the policies of “sanctuary” areas—cities, counties, or states that decline to aid ICE in the arrest of undocumented immigrants.

Local law enforcement agencies have no legal obligation to aid in civil immigration enforcement, but can voluntarily aid the federal government by complying with ICE detainers, or requests to hold the individual in question for up to 48 hours after their release date, giving ICE time to investigate and potentially arrest them.

Many of the hundreds of counties that decline to comply with ICE detainers do so on the grounds that extending the individual’s detention would arguably violate their Fourth Amendment rights. Furthermore, the partnership of local enforcement with ICE could foster distrust in the community, leading to fewer crimes reported by immigrants.

The Trump administration, however, frames the arrest of undocumented immigrants as a necessity to keep the U.S. safe, and stated in a January 2017 executive order that “it is the policy of the executive branch to empower State and local law enforcement agencies across the country to perform the functions of an immigration officer in the interior of the United States to the maximum extent permitted by law.”

ICE reported that 66% of the arrests made in 2018 were of convicted criminals, although the data does not specify the crime. Whether or not these arrests actually help the community, however, is a topic of ongoing debate. A handful of different studies have found that the number of undocumented immigrants in an area has no effect on violent crime, and is actually linked to lower rates of property crime.

A study by the Center for American Progress found that sanctuary counties see a lower crime rate and a higher median household income than non-sanctuary counties. According to the study, there are on average 35.5 fewer crimes committed per 10,000 people in sanctuary counties compared to non-sanctuary counties, and median household annual income is on average just over $4,000 higher. The poverty and unemployment rates are lower in these areas as well.

This would suggest that a separation between local law enforcement and ICE leads to greater prosperity in the community. The Major Cities Chiefs Association, a coalition of the chiefs and sheriffs in the largest cities, has supported this separation for many years. The association argued in a 2013 policy statement that having local police enforce federal immigration law “undermines the trust and cooperation with immigrant communities which are essential elements of community oriented policing.” They also voice concerns over resources, training, and a “lack of clear authority” that “increases the risk of civil liability for local police and government.”

Indeed, a 2014 case regarding an ICE detainer led to local governments paying a $120,000 settlement. Ernesto Galarza, a New Jersey-born U.S. citizen of Puerto Rican descent, was arrested in 2008 on drug charges for which he was later acquitted. Galarza posted bail the day after his arrest, but the local police held him for three more days in compliance with an ICE detainer filed due to a misguided tip. With representation from the American Civil Liberties Union of Pennsylvania, the courts found Galarza’s Fourth Amendment and due process rights had been violated.

Despite such occurrences, ICE is providing more opportunities for local law enforcement to get around sanctuary regulations and aid federal immigration enforcement with its new Warrant Service Officer program. Officers trained through the WSO program will be able to serve administrative warrants and execute an arrest on behalf of ICE, but only within the jail in which they work. ICE must take the arrested individual into custody within 48 hours, or they will be released.

The program allows smaller jurisdictions to partner with ICE without violating state or county regulations against compliance with ICE detainer requests—regulations acting ICE Director Matthew Albence said “undermine public safety, prevent the agency from executing its federally mandated mission and increase the risks for officers forced to make at-large arrests in unsecure locations.”

“The WSO program will protect communities from criminal aliens who threaten vulnerable populations with violence, drugs and gang activity by allowing partner jurisdictions the flexibility to make immigration arrests in their jail or correctional facility,” he said in a statement.

The WSO program is a step down from the 23-year-old 287(g) program, which allows partnered law enforcement agencies to conduct additional immigration enforcement activities such as questioning and processing. According to ICE, the department has 287(g) agreements with 80 law enforcement agencies in 21 states.

These programs allow law enforcement to act on behalf of ICE at the local level, despite the number of studies and professional dissent arguing in favor of a separation between local law enforcement and ICE. ICE still maintains that these sanctuary policies make communities less safe.

The WSO program is “an aid to the mission of the agency,” a Boston spokesman for ICE told Fortune, “especially in jurisdictions that have taken the misguided ‘sanctuary city’ policy approach, which only increases, not decreases, threats to the public safety.”

Due to ongoing litigation, ICE declined to comment on the Massachusetts courthouse arrests case. Its website, however, argues that courthouse arrests are safer for the officers, the arrestee, and the community “because courthouse visitors are typically screened upon entry to search for weapons and other contraband.”

Middlesex County District Attorney Marian Ryan, one of the plaintiffs in the Massachusetts case, argued otherwise, saying in a statement that the judicial system can only keep the public safe if it can prosecute criminal cases.

“ICE’s using state courthouses as a forum to conduct their enforcement work has struck fear in many of our most vulnerable, keeping them from accessing our courts,” she said in a statement announcing the lawsuit. “That is not justice. It does not make our communities safer.”