SAN FRANCISCO ― The Trump administration will go after undocumented immigrants in their neighborhoods and at work in California, likely picking up “collateral” they were not initially targeting, after the state’s new “sanctuary” law goes into effect, Immigration and Customs Enforcement Director Tom Homan said Friday.

His statement was a condemnation of the law, which Democratic Gov. Jerry Brown signed on Thursday, but also reads like a threat to undocumented immigrants in California. While the law was passed to protect them, ICE is now saying they are even more at risk of deportation and being separated from their families.

“ICE will have no choice but to conduct at-large arrests in local neighborhoods and at worksites, which will inevitably result in additional collateral arrests, instead of focusing on arrests at jails and prisons where transfers are safer for ICE officers and the community,” Homan said in a statement. “ICE will also likely have to detain individuals arrested in California in detention facilities outside of the state, far from any family they may have in California.”

California has the largest population of undocumented immigrants of any state with an estimated 2.3 million living there.

The new law will block local and state law enforcement from “using resources to investigate, interrogate, detain, detect, or arrest persons for immigration enforcement purposes.” Those purposes include making arrests on immigration warrants, detaining people solely at the request of federal immigration officials and inquiring into someone’s immigration status. The law goes into effect in January.

Jonathan Ernst/Reuters Immigration and Customs Enforcement acting director Tom Homan says "sanctuary" policies make cities less safe.

Though introduced prior to President Donald Trump’s inauguration, the legislation is also a direct response to the president’s promised crackdown on undocumented immigrants.

“These are uncertain times for undocumented Californians and their families, and this bill strikes a balance that will protect public safety, while bringing a measure of comfort to those families who are now living in fear every day,” Brown said in a signing statement.

While the bill was softened from its original version to allow some cooperation between local law enforcement and federal immigration officials in specific circumstances, the state’s influential sheriffs’ association remained opposed to it.

“Our overarching concern remains that limiting local law enforcement’s ability to communicate and cooperate with federal law enforcement officers endangers public safety,” the California State Sheriffs’ Association said in a statement. “The bill still goes too far in cutting off communications with the federal government.”

ICE officials argue that carrying out arrests in jails is both safer and more efficient than other methods, because the individuals are already in custody after arrest. Homan said the California law “will undermine public safety and hinder ICE from performing its federally mandated mission.”

But police-immigration enforcement cooperation has come under fire on both constitutional and public safety grounds. Critics ― including law enforcement leaders ― say that ICE working with police makes some local communities less likely to come forward to report crime or as witnesses out of fear about revealing immigration status, and could encourage racial profiling.

Those concerns led to “sanctuary” policies ― a loose term for jurisdictions that do not fully cooperate with ICE, often by declining to hold people on its request if it would otherwise release them. Courts have ruled in the past that police violated individuals’ constitutional rights by holding them based on an ICE request without a warrant.

Jurisdictions are not required by law to hold people on ICE’s behalf, but cannot have policies forbidding officials and law enforcement from sharing information with the federal government about immigration status.

The Trump administration has gone on an all-out assault on “sanctuary” policies, through executive orders, funding threats and public speeches claiming they are leading to increased violent crime. In April, a federal judge temporarily blocked Trump’s executive order threatening to pull funds for cities based on their sanctuary policies, but the Department of Justice has since put immigration conditions on grants.

Since the first major series of arrests carried out by the Trump administration, ICE has increased the number of “collateral” arrests of undocumented immigrants without serious criminal records who happened to be present while agents were arresting other people. The change marks a major break from practice during the Obama administration, which prioritized arresting those with serious criminal histories or prior deportations on their records.

ICE carried out a round of 498 arrests last week that specifically targeted “sanctuary” jurisdictions, including New York, Los Angeles and Denver. More than one-third of those arrested had no criminal convictions, according to ICE.

Trump officials — chiefly, Attorney General Jeff Sessions, who called the California law “unconscionable” — have hinted that a legal challenge may be on the horizon, a possibility California bill author State Senate President Pro Tem Kevin de León says he is prepared for. On Thursday, however, the White House declined to get into specifics on how the administration plans to respond.

“We are spending every day we can trying to find the best way forward; the president will be laying out his responsible immigration plan over the next week,” said White House press secretary Sarah Huckabee Sanders. “I hope that California will push back on their governor’s ... irresponsible decision moving forward.”

Roque Planas contributed reporting.