The Department of Justice on Oct. 15 proposed a rule that would enable the DNA collection of noncitizens in immigration detention and the transfer of that information into a national criminal database. The rule would affect the more than 40,000 people currently held in immigration detention facilities. Civil rights groups have already warned that the rule may implicate serious privacy concerns and denigrates the civil rights and liberties of the most vulnerable.

Here is what we know so far:

It may be surprising that the attorney general already has the authority to collect DNA samples from noncitizens in detention under the DNA Fingerprint Act of 2005 (as well as from those who have been arrested, are facing charges or have been convicted). But, through an exemption, the secretary of homeland security has the authority to halt DNA collection. Since the law’s enactment in 2005, the secretary has utilized this exemption.

The rationale behind the exemption originated in the rise of immigration detention in the United States. In the late 1990s, the detention of noncitizens expanded massively, and, as a result, Congress created an exemption to the act in 2008. The exemption, § 28.12(b)(4), applied to noncitizens specifically and allowed the secretary of homeland security, in consultation with the attorney general, to refrain from applying the act if it was determined such DNA collection was unfeasible “because of operational exigencies or resource limitations.” In other words, Congress recognized that collecting DNA from thousands of detained immigrants would cost a lot of money and run into implementation problems.

In fact, then-Secretary of Homeland Security Janet Napolitano wholeheartedly embraced the exemption. On March 22, 2010, she wrote a letter to then-Attorney General Eric Holder stating that, due to the sheer volume of individuals falling within the targeted class, implementation posed “severe organizational, resource, and financial challenges.” At the time, approximately 30,000 noncitizens were held in detention. Aware of the public outcry likely to ensue, Napolitano also suggested the exemption would ameliorate any privacy or civil liberties concerns. Napolitano and Holder formalized an agreement to allow the exemption to hold. The waiver applied to two groups: individuals in immigration custody not charged with a crime and individuals in detention awaiting deportation proceedings.

But a Homeland Security official has told news sources that the department now believes the exemption is outdated, and the new rule published in October says that DNA collection is feasible. Because of the “fundamental changes in the cost and ease of DNA-sample collection,” the drafters of the proposed rulemaking suggest that DNA-sample collection from persons taken into or held in custody “is no longer a novelty.” According to the proposal, well-established methods used to collect DNA from persons arrested or held on criminal charges can also be applied to those in detention. As currently imagined, Immigration and Customs Enforcement (ICE) plans to use Rapid DNA testing—a form of DNA testing that collects skin cells from a cheek swab—and store those samples in the FBI’s DNA database, “a tool for linking violent crimes” known as CODIS.

In proposing to lift the exemption, the rule does not address the privacy or civil liberties concerns that Napolitano raised in 2010. However, it does state that making the distinction between criminal arrestees and immigration detainees is “largely artificial” because “most immigration detainees are held on the basis of conduct that is itself criminal.”

While ICE has published standards that instruct officers to conduct pat searches of detainees on a routine basis and without suspicion, called Performance-Based National Detention Standards 2011 (PBNDS), the courts have not addressed the constitutionality of such searches in the civil immigration detention context. DNA testing, by contrast, is referenced in the “Body-Cavity Search” subheading of the PBNDS—which is considered, according to the standards, “the most intrusive type of search.” The standards suggest that DNA testing performed on a sample of blood requires both informed, written consent and reasonable suspicion.

Legal challenges to the rule will likely have to overcome some thorny hurdles. Even though legal precedent has established that constitutional protections apply to noncitizens, an exception under the Fourth Amendment gives administrative agencies, in furtherance of national security, wide berth to search individuals within a 100-mile zone of the border. In instances where courts are compelled to weigh national security interests against civil liberties concerns, national security concerns usually win out.

Beyond the 100-mile zone, the collection of DNA samples from arrestees or from nonviolent felons on probation, parole or supervised release are permissible under the Fourth Amendment. In Maryland v. King, the Supreme Court found that a state statute authorizing warrantless DNA collection from individuals who had been arrested for serious offenses was constitutional under the Fourth Amendment. In arriving at its conclusion, the court determined that the need for a warrant for this kind of search was “greatly diminished,” since “the arrestee was already in valid police custody for a serious offense supported by probable cause.”

While the Maryland court gave great weight to the need of law enforcement officers to identify a person and possessions taken into custody, it believed that the intrusions on an individual’s privacy, in contrast, were minimal. The court also reasoned that the expectations of privacy for such individuals in criminal custody were already diminished. Moreover, a swab inside a person’s cheek posed no threat to an individual’s health or safety. The Maryland court also likened DNA testing to fingerprinting. Fingerprinting was already a ubiquitous practice by the time the Maryland decision was handed down in 2013. Maryland has opened the door for lower courts to extend DNA collection to those who have been convicted for misdemeanor offenses.

Future challenges will likely distinguish between immigrant individuals held in detention pursuant to the Immigration and Nationality Act and those held in custody because they have been arrested or convicted of a criminal offense. The Fourth Amendment prohibits searches and seizures executed without a warrant or probable cause, and Maryland carved out an exception for such searches only for those held in police custody on criminal charges—since the arrest of these individuals has already been supported by probable cause. The proposed rulemaking at issue suggests DNA collection of immigrant detainees should be justified because the government already collects such evidence from criminal arrestees. But probable cause is nonexistent for those held in immigration detention custody. In fact, many immigrants held in detention do not have criminal convictions and are merely held on civil immigration offenses such as unlawful presence or visa overstay.

This proposed rule is one of many the Trump administration has put forward over the past several months that would profoundly shape and restrict immigration to the United States. The Department of Homeland Security has announced plans to hike fees for USCIS applications, ask noncitizens for social media handles in USCIS forms to vet applications, and limit access to work authorization for asylum seekers with pending applications, to name a few. Just a few weeks ago, the department proposed to return asylum seekers to certain countries that have negotiated bilateral agreements with the U.S., including Guatemala, Honduras and El Salvador.

Courts have tested the legality of some of these regulations. Last month, three federal judges in New York, California and Washington state blocked Homeland Security’s “public charge” rule, a regulation that would impede the ability of immigrants who rely on public benefits to qualify for permanent residency. Though the U.S. Courts of Appeals for the 4th and 9th Circuits have recently lifted the injunction, a separate nationwide order prevents the rule from going into effect. The fight over the legality of the third-country rule, which limits access to asylum for noncitizens based on the manner in which they reach the United States, is also currently being played out by the courts.

The public submitted over a thousand comments in response to the proposed rule to collect DNA from immigrant detainees. Now that the notice-and-comment period has closed, the Department of Justice is legally obligated to consider and respond to all substantive comments and revise the proposed rule accordingly. This process could take as little as a few months, or it could take as long as a year. Once on the books, the final rule will then need to clear legal hurdles that immigration advocates will very likely mount.