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Immigrant advocates are being arrested in front of the White House fence, after sitting down and defying orders from police.

About three dozen protesters and U.S. Rep. Luis Gutierrez of Illinois joined in the civil disobedience Saturday. They held a sign saying, "Obama, Stop deporting our Families." Some wore T-shirts that read "Arrest us, Not our Families."

Protesters are usually required to stay in motion when demonstrating in front of the White House.

Hundreds of protesters turned out for the rally at Lafayette Park, urging President Obama to fulfill his campaign promises to achieve immigration reform.

Obama was to return to the White House around 2:40 p.m. after speaking at the University of Michigan. Two Marine helicopters flew overhead, but it wasn't clear if Obama was on board.

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Obama had once promised to tackle immigration reform in his first 100 days, but has pushed back that timetable several times. He said this week that Congress may lack the "appetite" to take on immigration after going through a tough legislative year. However, the president and Congress could address related issues, like boosting personnel and resources for border security, in spending bills this year.

Activists said outrage over Arizona's controversial immigration law "awakened a sleeping giant" Saturday as rallies demanding federal immigration reform kicked off in cities across the country.

In New York, Labor organizer John Delgado said anger over the law -- which requires local law enforcement to question people about their immigration status if there is reason to suspect they're in the country illegally -- drew more than 5,000 people to a rally at Manhattan's Foley Square.

"That's the fuel that motivated them to come here, because of the sadness of the Arizona law," said Delgado, who is business manager for Local 79 of the Construction and General Building Laborers Union.

Organizers believe opposition to the law could be the catalyst to draw tens of thousands to rallies in dozens of cities. Four years ago, more than a million people across the country united to protest ultimately unsuccessful federal legislation that would have made being an illegal immigrant a felony.

The movement fractured and annual May 1 rally attendance dropped sharply as attempts to reform federal immigration policy fizzled. In 2006, nearly half a million people took to Chicago's streets. Last year, fewer than 15,000 participated in the rallies, held May 1 because it's a traditional day of protest and International Workers Day.

But immigration reform advocates have seen a flurry of activity since Republican Gov. Jan Brewer signed the Arizona measure into law last week.

"What happened in Arizona proves that racism and anti-immigrant hysteria across the country still exists. We need to continue to fight," said Lee Siu Hin, a coordinator with the Washington, D.C.-based National Immigrant Solidarity Network.

Relying on online social networking, churches and ethnic media to mobilize, activists have called for a boycott of Arizona businesses and protested outside Arizona Diamondbacks baseball games.

Supporters say the law is necessary because of the federal government's failure to secure the border, and they pointed to an attack Friday on a sheriff's deputy in southern Arizona as proof something had to be done.

The Pinal County Sheriff's Office said Deputy Louie Puroll was shot and wounded after coming across a band of suspected drug smugglers about 50 miles south of Phoenix. Brewer and others immediately chimed in, saying the attack shows a growing problem with a porous border.

"The horrendous violence we see by narco-terrorists is uncontrolled, and our own federal government refuses to fulfill its responsibility to secure our border," Brewer said in a statement.

Critics of the law say it's unconstitutional and encourages racial profiling and discrimination against immigrants or anyone thought to be an immigrant. But they say that without federal legislation in place to address the estimated 12 million illegal immigrants living in the U.S., other states may follow Arizona's lead.

"If Republicans and Democrats do not take care of this albatross around our necks, this will in fact be the undoing of many, many years of civil rights struggle in this country," said Jorge-Mario Cabrera, a spokesman for the Coalition for Humane Immigrant Rights of Los Angeles, where organizers expect 100,000 to march downtown Saturday.

Activists aren't alone in their opposition to Arizona's law, a fact May 1 organizers hope will draw out even more people Saturday.