A federal judge has temporarily blocked immigration officers in Southern California from making warrantless arrests unless they can show the person is likely to escape. In a preliminary injunction issued on September 2 and unsealed this week, U.S. District Judge Maame Ewusi-Mensah Frimpong ruled that the government must evaluate all known circumstances before making a civil immigration arrest without a warrant. The ruling comes after a lawsuit filed last fall by the American Civil Liberties Union (ACLU) of Southern California, Public Counsel, and local immigrant advocacy groups, who raised concerns during a period of heightened immigration enforcement in the region. The order applies to the Central District of California, which includes Los Angeles, Orange, Riverside, San Bernardino, Ventura, Santa Barbara, and San Luis Obispo counties. Judge Frimpong also required the government to thoroughly document the probable cause for any arrest before a warrant could be obtained. She emphasized that being in the country illegally is not, on its own, enough to justify a warrantless arrest. "Without this, Defendants cannot show that any arrest was proper," she wrote in her order. The government requested a delay to appeal the ruling, but Frimpong denied the request. The lawsuit also aimed to stop immigration officers from conducting stops and arrests based on race, language, or occupation, and to ensure people in detention have access to legal counsel. Judge Frimpong had previously issued a temporary restraining order to limit these large-scale immigration operations, but the U.S. Supreme Court lifted it last September. Justice Brett Kavanaugh noted that ethnicity could be a factor in a stop if combined with other information. Federal judges in Portland, Colorado, Washington, D.C., and the Eastern District of California have already blocked similar warrantless arrest practices. Plaintiffs argued that in many arrests they tracked, officers failed to document the likelihood of escape. In response, a federal attorney for the government, Daniel Mummolo, said there was no legal requirement to document such assessments, and that officers might handle the process differently. However, Judge Frimpong pointed out that a 2026 memo from a former immigration official suggested officers could make "on-the-spot" escape risk assessments. She noted that no evidence was presented that officers had actually done so. The plaintiffs' attorney, Laura Perry Stone, argued that the memo required officers to assess both the likelihood of the person fleeing and their ability to be located elsewhere, such as at home or work. Judge Frimpong found that government records, including agent depositions and video evidence, showed that current practices often relied on unlawful status or false claims rather than proper assessments. In one case, the government claimed an individual was running away from agents, but video showed him walking normally and texting before being questioned. Mayra Joachin, an attorney with the ACLU of Southern California, said the ruling should stop numerous unlawful arrests in the region. "We will closely monitor compliance with this court order, and expect the federal government to abide by it," she said.