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 that President 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.

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 from 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 Arizona Gov. Jan Brewer signed the legislation April 23. Supporters say the law, which makes it a state crime to be in the U.S. illegally, is necessary because of the U.S. government’s failure to secure the border, but critics claim it encourages racial profiling and is unconstitutional.

“It’s racist,” said Donna Sanchez, 22, a 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.”

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

Obama once promised to tackle immigration reform in his first 100 days, but he has pushed back that timetable several times. He said last 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, such as boosting personnel and resources for border security, in spending bills this year.

Juan Haro, 80, was born and raised in Denver, where about 3,000 people rallied. Haro, who said his family is originally from Mexico, thinks Arizona’s new law targets Mexicans specifically.

“This country doesn’t seem to be anti-immigrant,” he said. “It seems to be anti-Mexican.”

At the White House, U.S. Rep. Luis Gutierrez, D-Ill., was arrested with several others in a demonstration of civil disobedience against the Arizona law.

In Dallas, police estimated at least 20,000 attended a rally.

Among them was Juan Hernandez, the Hispanic outreach coordinator for Sen. John McCain’s unsuccessful presidential run. He said Arizona was once deemed by those south of the border to be a model state with particularly close ties to Mexico.

“It went beyond what most states do,” he said. “Now they are a state that goes beyond what the Constitution says you should do.”

About 12 people at the Dallas event carried signs depicting Brewer as a Nazi and Maricopa County Sheriff Joe Arpaio, known for his tough illegal immigration stance, as a Klansman. Organizers were asking sign holders to discard the placards.

A smattering of counterprotesters attended rallies. In Tucson, Ariz., a few dozen people from the group Arizonans For Immigration Control showed up in support of the new law and Brewer.