Chicago ? Angered by a controversial Arizona immigration law, tens of thousands of protesters — including 50,000 alone in Los Angeles — rallied in cities nationwide demanding President Barack Obama tackle immigration reform immediately.

“I want to thank the governor of Arizona because she’s awakened a sleeping giant,” said labor organizer John Delgado, who attended a rally in New York where authorities estimated 6,500 gathered.

From Los Angeles to Washington D.C., activists, families, students and even politicians marched, practiced civil disobedience and “came out” about their citizenship status in the name of rights for immigrants, including the estimated 12 million living illegally in the U.S.

A congressman was among 35 people arrested during a protest at the White House. U.S. Rep. Luis Gutierrez, D-Ill., was taking part in a civil disobedience demonstration.

Protests elsewhere were largely peaceful. No arrests were reported at most demonstrations; two were arrested near the march route in Los Angeles, but police said neither suspect appeared to be connected to the rally.

Police said 50,000 rallied in Los Angeles where singer Gloria Estefan kicked off a massive downtown march. Estefan spoke in Spanish and English, proclaiming the United States is a nation of immigrants.

“We’re good people,” the Cuban-born singer said atop a flatbed truck. “We’ve given a lot to this country. This country has given a lot to us.”

Public outcry, particularly among immigrant rights activists, has been building since last week when Arizona Gov. Jan Brewer signed the legislation. The law requires local and state law enforcement to question people about their immigration status if there’s reason to suspect they’re in the country illegally. It also makes it a state crime to be in the United States illegally.

The law’s supporters say it’s necessary because of the federal government’s failure to secure the border, but critics contend it encourages racial profiling and is unconstitutional.

“It’s racist,” said Donna Sanchez, a 22-year-old U.S. citizen living in Chicago whose parents illegally crossed the Mexican border. “I have papers, but I want to help those who don’t.”

Obama 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, Obama and Congress could address related issues, like boosting personnel and resources for border security, in spending bills this year.

Organizers estimated about 20,000 gathered at a park on Chicago’s West Side and marched, but police said about 8,000 turned out.

The event resembled something between a family festival — food vendors strolled through with pushcarts — and a political demonstration with protesters chanting “Si se puede,” Spanish for “Yes we can.” A group of undocumented students stood on a stage at the Chicago park and “came out” regarding their immigration status.