On Tuesday night, U.S. Immigration and Customs Enforcement arrested more than 150 people in Northern California suspected of being undocumented immigrants. More than 850 others, immigration officials said, slipped through their fingers.

That large number is being blamed on the actions of Oakland’s mayor, Libby Schaaf, who on Saturday made the controversial decision to go on television to warn the immigrant community in Oakland that she had heard from “multiple credible sources” that ICE was preparing an immediate, large-scale immigration raid in the Bay Area.

“My priority is for the well-being and safety of all residents — particularly our most vulnerable,” she said in a statement. She also directed undocumented immigrants and their friends and family to a resource about their rights.

ICE Deputy Director Thomas Homan condemned Schaaf’s “irresponsible” actions, saying in a statement Wednesday that “sanctuary jurisdictions like San Francisco and Oakland shield dangerous criminal aliens from federal law enforcement at the expense of public safety. … The Oakland mayor’s decision to publicize her suspicions about ICE operations further increased [the] risk for my officers and alerted criminal aliens—making clear that this reckless decision was based on her political agenda with the very federal laws that ICE is sworn to uphold.”

Homan also asserted that “ICE does not conduct sweeps or raids that target aliens indiscriminately, and the agency prioritizes public and national security threats, immigration fugitives and illegal reentrants.” However, roughly half of the immigrants rounded up in the raid had no criminal convictions.

Schaaf, who worked on deportation cases as an attorney earlier in her career and who has said she felt a moral obligation to warn residents, told the Washington Post on Tuesday that she made the decision as part of the resistance to the Trump administration’s immigration enforcement policies.

She told the Post that because she found out about the sweep through unofficial sources and not government channels, she does not think she obstructed justice or broke the law. At least one former federal prosecutor disagrees.