A city becomes a sanctuary city by adopting its own local policies that limit how municipal employees and police cooperate with federal immigration enforcement. There is no application, no federal or state agency that grants the status, and no official designation to earn. A city council passes an ordinance, a mayor signs an executive order, or a police chief issues a departmental directive — and the city is, in substance, a sanctuary jurisdiction. Hundreds of cities and counties have taken this step using ordinary tools of local government.
The Legal Basis That Makes It Possible
Sanctuary policies rest on the anti-commandeering doctrine, grounded in the Tenth Amendment. In Printz v. United States (1997), the Supreme Court held that Congress cannot force state or local officials to carry out federal programs. The case involved firearm background checks, but the principle applies broadly: the federal government can enforce its own laws with its own agents, but it cannot conscript local police or city staff to act as federal immigration officers.
This is why sanctuary policies are legally viable. Cities aren’t blocking ICE. ICE agents remain free to operate inside any jurisdiction. What the city does is decline to volunteer local resources for that work. Courts have treated that distinction — non-participation rather than obstruction — as constitutionally protected.
The Three Tools a City Uses
Sanctuary status is created through one or more of three local instruments, each with different strengths.
Municipal Ordinance
An ordinance is a local law passed by the city council with binding legal force. It can prohibit city employees from using municipal funds or resources to assist federal immigration enforcement. Because it is codified law, it survives changes in political leadership. Several major cities have moved from informal practice to a formal ordinance specifically to keep a future mayor or police chief from reversing course on their own. This is the most durable route.
Resolution
A resolution is a formal statement by the city council expressing intent or political position. It does not carry the same weight as an ordinance, but it serves as a public declaration and can direct city agencies to develop internal procedures consistent with the council’s stance. Many cities that eventually passed ordinances began with a resolution.
Executive Order or Departmental Directive
An executive order from the mayor, or a directive from a department head such as the police chief, is the fastest option. It binds employees within that department and can change operating procedures immediately. The tradeoff is fragility: a successor can rescind it on day one, and that has happened in several jurisdictions after local elections.
In practice, most cities combine these. A police chief might issue an immediate directive while the council works on permanent legislation, with the mayor publicly signaling that a veto is unlikely.
What the Policy Actually Says
The word “sanctuary” covers a range of policies, and no two jurisdictions are identical. Most cluster around a handful of core provisions, and a city becoming a sanctuary generally picks from this menu.
Declining ICE Detainer Requests
When ICE identifies someone in a local jail it believes is removable, it sends a detainer request on Form I-247A asking the jail to hold that person for up to 48 hours past their scheduled release so ICE agents can pick them up.1ICE. Immigration Detainer – Notice of Action Detainers are not warrants and not judicial orders; the form itself uses the word “requested.”
Sanctuary jurisdictions often decline these requests. Holding someone past their release date without a judge’s approval raises Fourth Amendment problems, and multiple federal courts have ruled that jails honoring detainers without a judicial warrant can be held liable for violating inmates’ rights. Many jurisdictions will extend custody only when ICE produces an actual judicial warrant. The federal government has pushed back, with the Department of Homeland Security formally notifying jurisdictions that refuse to honor detainers.2U.S. Department of Homeland Security. DHS Puts California, New York, and Illinois on Notice for Failure to Honor Criminal Illegal Alien Detainers
Limits on Immigration Status Inquiries
Many sanctuary jurisdictions bar local officers from asking about immigration status during routine encounters like traffic stops, calls for service, or witness interviews. The rationale is practical: when undocumented residents fear that any police contact could lead to deportation, they stop reporting crimes, stop cooperating as witnesses, and stop calling 911. Police departments adopting these rules usually frame them as community policing.
Restrictions on Information Sharing
Some ordinances go further and restrict sharing personal details such as home addresses and workplace locations with federal immigration authorities. Federal law at 8 U.S.C. § 1373 prohibits local governments from restricting the sharing of immigration status information with federal authorities.3Office of the Law Revision Counsel. 8 USC 1373 – Communication Between Government Agencies and the Immigration and Naturalization Service Sanctuary cities generally argue their policies comply with § 1373 because they restrict sharing of personal information like addresses, not status itself. That distinction remains contested in court.
Protections for Schools, Clinics, and Courthouses
Sanctuary policies often extend beyond policing. Building on Plyler v. Doe (1982), which held that public schools cannot deny enrollment based on immigration status, many cities prohibit school staff from collecting data on students’ status or place of birth, require a judicial warrant before ICE can enter school grounds, and route any federal enforcement inquiries through district legal counsel.4Justia U.S. Supreme Court Center. Plyler v. Doe, 457 US 202 (1982) Similar provisions can cover municipal health clinics and local courthouses, so residents don’t skip hearings or avoid seeking protective orders out of fear of enforcement. ICE’s own interim guidance acknowledges that jurisdiction-specific limits may restrict courthouse arrests and instructs agents to coordinate with local legal advisors first.5ICE. Protected Areas and Courthouse Arrests
Whether the City Calls Itself a Sanctuary
Some cities announce sanctuary status openly, writing the label into ordinances and making it a public commitment. Others adopt identical policies without ever using the word. Legally, substance is what counts. A city that quietly declines detainers and restricts information sharing is functionally a sanctuary jurisdiction whether it claims the title or not. The choice is largely political: using the label signals solidarity to immigrant communities, but it also invites federal attention and funding disputes.
Implementation After the Vote
Passing the ordinance or issuing the directive is the start, not the finish. City employees need training on the new procedures. Departments need protocols for handling ICE requests and responding when federal agents arrive at a city facility. Police departments usually revise policies on when officers may inquire about status, how to handle detainer requests, and how to route federal enforcement inquiries. Reporting mechanisms have to exist so the city knows whether its own rules are being followed.
State Laws Can Override the City
Roughly 20 states have passed laws that prohibit local sanctuary policies or require local agencies to cooperate with federal immigration enforcement to some degree. Scope varies. Some narrowly require jails to honor ICE detainers. Others broadly forbid any local rule that limits cooperation with federal agents.
Consequences vary too. Courts can invalidate a sanctuary ordinance and permanently enjoin its enforcement. Officials who knowingly violate cooperation mandates can face civil fines per incident, and in the most aggressive states, elected officials can be suspended from office by the governor. Some states also bar the use of public funds to defend officials found to have willfully violated cooperation requirements. If you are in a preemption state, a city council vote alone may not be enough to sustain the policy.
Federal Funding Pressure
The federal government’s main lever against sanctuary jurisdictions is money. It has attempted to condition law enforcement grants, particularly the Edward Byrne Memorial Justice Assistance Grants, on compliance with § 1373 and on additional conditions requiring advance notice of inmate release dates and ICE access to local jails. Section 1373 itself does not require local officials to ask about status, share criminal history records, notify ICE of release dates, or honor detainers; the gap between the statute’s text and the conditions the federal government has attached to grants is where much of the litigation sits.
An April 2025 executive order directed the Attorney General and the Secretary of Homeland Security to publish a list of sanctuary jurisdictions and instructed federal agencies to identify grants and contracts that could be suspended or terminated.6The White House. Protecting American Communities from Criminal Aliens A federal judge in the Northern District of California issued a preliminary injunction blocking the government from withholding or conditioning federal funds based on a jurisdiction’s sanctuary policies, relying on the same anti-commandeering principle from Printz. The boundaries of permissible federal pressure are still being litigated, so a city adopting sanctuary policies should expect its status to be tested both in court and through funding disputes for the foreseeable future.