Prior convictions for certain felonies, including placement on the state's sex offender or arson registries, would also allow the suspect to be held. Crimes that would not be considered serious enough to trigger the hold include simple possession of marijuana and selling food on the street without a permit.

Ammiano introduced the bill to counter the federal Secure Communities program, which was created to deport dangerous criminals. But the assemblyman said the program was used to deport nearly 100,000 Californians, the vast majority of whom, he said, were not serious offenders.

"With the Trust Act, Gov. Brown is recognizing the importance of immigrants to the economy, culture and vitality of the entire state," Ammiano said.

The bill is still opposed by the California State Sheriffs Assn. and the California District Attorneys Assn.

Mark Zahner, chief executive for the prosecutors group, said it was disappointed the bill was signed.

The district attorneys opposed the measure because "it didn't foster cooperation between federal and state officers." He also said there were questions about whether the measure could be preempted by federal immigration law.

Word of the governor's action spread quickly through the several thousand marchers pressing for immigration reform at a rally in Hollywood — one of many held in cities around the nation Saturday.

"This is exactly what we're looking for," Jorge Garavito, 22, of Rialto shouted over the roars of marchers on Vine Street. "The governor is recognizing the power of the people, and that this is what the people want."

"Families no longer have to live in fear," said marcher and union leader Oscar Valladares, 34. "Children will know that at the end of the day, they're going to see their parents."

Two measures signed Saturday target employers who retaliate against employees by threatening to report immigration law violations. Assemblyman Kevin Mullin (D-South San Francisco) said he introduced AB 524 to prevent employers from using the reporting threat to stop workers from complaining about workplace abuses, unsafe working conditions and wage theft.

Senate leader Darrell Steinberg (D-Sacramento) addressed the same issue with SB 666, under which an employer's business license could be suspended or revoked for retaliation against workers based on immigration status.

The governor also signed a bill by Assemblywoman Lorena Gonzalez (D-San Diego) that removes immigration status as a barrier to becoming licensed as an attorney for any applicant who has passed the state bar exam.

Gonzalez introduced AB 1024 in response to a case pending before the California Supreme Court involving Sergio C. Garcia, who passed the bar exam and met all other requirements but is in the country illegally.

The bill "completes the promise we've made," Gonzalez said, to immigrants "who have worked hard, studied hard, passed the bar exam and now just want the right to make a living for themselves as an attorney."

Times staff writers Matt Stevens and Cindy Chang in Los Angeles and Melanie Mason in Sacramento contributed to this report.