The Justice Department is pushing as a part of its budget proposal to change federal law so that local jurisdictions can be forced to detain suspected illegal immigrants upon request.
The move would give the administration far more leeway to make good on its promise to crack down on "sanctuary cities" - although it would surely meet resistance from some local law enforcement agencies that do not want their officers used to enforce immigration law.
"Having states and local jurisdictions enforce federal immigration law terrorizes immigrant communities and makes the whole community less, not more, safe, as police chiefs around the country recognize," said Lee Gelernt, deputy director of the ACLU's national Immigrants' Rights Project.
The measure - a small portion of the budget proposal and readily confirmed by Justice Department officials - is unlikely to become reality. The budget request still must be evaluated by Congress, and lawmakers are likely to change it substantially. But the request demonstrates the lengths to which the Justice Department is willing to go to beef up immigration enforcement.
The Justice Department also asked for more authority to tie grant money to local jurisdictions' cooperation with immigration enforcement.
President Donald Trump signed an executive order - which has since been blocked by a federal judge - threatening to cut the flow of federal funds to "sanctuary cities." Attorney General Jeff Sessions later sent letters to nine jurisdictions asking them to produce proof that they are communicating with federal authorities about undocumented immigrants or risk losing money.
But federal law limits the authority of the president and the attorney general to take real action. The law says only that cities must not restrict information sharing with Immigration and Customs Enforcement. It does not mention instances in which the federal government learns that a person in local custody might be in the country illegally and asks a jurisdiction to detain that person.
Some city officials are reluctant to honor such detainer requests because the federal government is not willing to reimburse them, and they worry about the legal implications of holding people on immigration offenses without criminal warrants.
Local law enforcement officials also worry that if they are perceived as agents of Immigration and Customs Enforcement (ICE), witnesses and others might be less willing to cooperate with them in other kinds of investigations for fear of being deported.
Justice Department officials have said that under current law, holding illegal immigrants upon request is voluntary. And in a memo Tuesday, Sessions seemed to concede that his power in the matter was limited.
He declared that sanctuary cities, even under Trump's executive order, were only those places that violated the particular federal law that stops local officials from putting any restrictions on information sharing with ICE. Only such jurisdictions, he said, were at risk of losing federal funding.
If the Justice Department's proposal were to become law, though, all jurisdictions that do not honor detainer requests will be at risk. The law would block cities from enacting policies that stop compliance with legal Department of Homeland Security requests, including "any request to maintain custody of the alien for a period not to exceed 48 hours."
The state of Texas recently passed a bill that imposes fines and even jail time on local authorities who do not cooperate with ICE agents.
The Washington Post's Sari Horwitz, Kelsey Snell and Maria Sacchetti contributed to this report.