As more states map out their own immigration stands, California is taking its fight against mass deportation to a new level by restricting communication about release dates that help federal authorities arrest prisoners for deportation.

The Associated Press Protesters at a San Francisco rally opposing deportation of unauthorized immigrants. Gov. Jerry Brown, a Democrat, recently signed a law making California a sanctuary state.

As more states and counties take immigration policy into their own hands, California is stepping up its fight to protect unauthorized immigrants by not only refusing to detain immigrants slated for deportation, but now also by declining to tell federal immigration officials when they will be released from local jails.

Advocates say it’s the next logical step in defying the Trump administration’s expanding threats to deport more unauthorized immigrants. Such tactics have been tried in smaller jurisdictions — immigrant-friendly counties in Illinois, Massachusetts, New Jersey and Texas — but never by a whole state.

California’s new approach could have sweeping implications for Immigration and Customs Enforcement. The state has the lion’s share of unauthorized immigrants, and its action might prompt other states to defy the Trump administration’s quest to deport more of them.

U.S. Immigration and Customs Enforcement (ICE) has targeted nearly a million people for deportation. The number of ICE requests to local officials asking them to delay the release of jailed immigrants so that they may be deported was up 75 percent this year, according to ICE.

Many states and counties already limit their cooperation with these requests, known as detainers, out of a desire to protect immigrants or because of legal concerns about being sued for civil rights violations.

More than one-fifth of the unauthorized immigrant population in the United States resides in California, making it fertile ground for ICE officers. Since the enforcement agency began keeping records in 2003, some 23 percent of the agency’s detainers nationwide have been requested from California jails.

More than one-fifth of the unauthorized immigrant population in the United States resides in California.

The law that includes the policy shift, signed by Democratic Gov. Jerry Brown earlier this month, also bars California cities and counties from helping ICE by investigating the immigration status of prisoners when they book them. Orange County was the lone California jurisdiction participating in the 287(g) program.

Sheriffs, who run most of the state’s jails, largely oppose the new law, according to California State Sheriffs’ Association President Bill Brown. The law does not apply to immigrants who have committed serious crimes such as felonies and certain misdemeanors, but Brown would have liked exceptions for other crimes such as repeated driving while intoxicated or theft.

“This is not about law-abiding immigrants,” he said. “For the criminals, I don’t know why we wouldn’t want to take advantage of this opportunity to have that person removed from the community.”

Orange County Sheriff Sandra Hutchens agreed.

“Restrictions on our ability to communicate with federal authorities will hinder collaborative efforts to remove serious offenders from our community,” she said in a statement to Stateline.

The Trump administration’s reaction to the new law was swift.

Thomas Homan, acting director of ICE, said it would create “another magnet for more illegal immigration, all at the expense of the safety and security of the very people it purports to protect.”

The new law will keep ICE from arresting deportable criminals in the relative safety of county and city jails, forcing the agency to pursue prisoners in their neighborhoods and workplaces, which could result in violence, Homan said in a statement after the bill’s signing.

Democratic state Sen. Kevin de León of Los Angeles, the author of the new law, called Homan’s reaction “fearmongering” and pledged that “we won’t help them tear apart families and our economy in the process.” De Leon recently announced that he will challenge longtime U.S. Sen. Dianne Feinstein in next year’s Democratic primary.

California is the first state to limit communication about release dates, but 142 counties have such policies, according to a review by the Immigrant Legal Resource Center, a national advocacy group based in San Francisco.

California a Trailblazer

The federal government has challenged some of those policies on release dates. U.S. Attorney General Jeff Sessions this month accused Cook County and the city of Chicago in Illinois; New Orleans; New York City, and Philadelphia of violating federal law on cooperation. He has not yet responded to California’s new law.

Detainers work by taking advantage of a system already in place. When prisoners are booked into local jails, typically run by city police or county sheriffs, their information is automatically sent to ICE, which checks fingerprints and other details to see whether the prisoner is an unauthorized immigrant wanted for deportation.

If so, ICE can ask local authorities to hold the prisoner for up to 48 hours to allow ICE to take custody. Alternatively ICE can ask for notification of the prisoner’s release to facilitate an arrest.

Some states — Illinois, Connecticut, Vermont and Oregon — have statewide sanctuary legislation that limits cooperation on deportation, but stops short of California’s unusual scope. Fifteen states considered bills on sanctuary policies this year.

And a Massachusetts Supreme Court ruling this year prohibits holding prisoners on immigration detainers alone.

Other states have moved in the other direction. In Maine, where some state sanctuary policies were reversed in 2011 by Republican Gov. Paul LePage, the governor has threatened to remove sheriffs from office if they fail to honor detainers. Those seeking to stop sanctuary city policies and even force police to investigate immigration status include Alabama, Arizona, Georgia, North Carolina, Tennessee, Texas and Wisconsin.

At least 33 states have some legislation requiring police to cooperate with immigration authorities, according to an April report from the nonpartisan Migration Policy Institute.

In many places outside California, sanctuary city policies are meant to reassure immigrants but don’t necessarily do more than restate existing laws allowing local police to leave immigration enforcement to the federal government, said Muzaffar Chishti, director of the Migration Policy Institute’s office at New York University School of Law.

In Arizona, for instance, Republican Attorney General Mark Brnovich concluded earlier this month that new policies in Phoenix did not conflict with a state law banning sanctuary policies despite setting limits on immigration enforcement.

Supreme Court May Decide

Some local jails also have refused to give enough notice of release dates. Cook County, Illinois, home of Chicago, banned such communication in 2011. Along with counties in California, counties in Massachusetts, New Jersey and Texas have withheld release dates, said Jessica Vaughan, director of policy studies at the Center for Immigration Studies, which advocates decreased immigration.

“The sanctuary policies that prevent the communication or notification to ICE are deliberate efforts to thwart immigration enforcement,” Vaughan said.

The U.S. Supreme Court will likely decide whether policies like California’s and Cook County’s cross the line and violate federal law requiring cooperation with federal authorities on immigration, Chishti said.

Sessions set an Oct. 27 deadline for Cook County, New York City, Philadelphia and other areas to justify their policies.

“He’s asking them to say if they comply with the law,” Chishti predicted. “They will come back and say ‘yes, we do comply,’ and then it will all end up at the Supreme Court.”