(CNN) -- They came from Los Angeles and San Diego, and Wisconsin, Texas, Illinois, Chicago, Seattle and, of course, Arizona -- a river of humanity flooding the Phoenix streets to protest the state's controversial immigration law.
The Arizona legislature passed the bill earlier this year and the state's Republican governor, Jan Brewer, signed it. In two more months, unless the law is overturned in court, police in Arizona will be allowed to check the residency status of anyone who is being investigated for a crime or possible legal infraction if there is reasonable suspicion the person is in the United States illegally.
Opponents say the bill opens the door for racial profiling. Supporters deny that and say it's necessary to stem a tide of illegal immigration they believe is a source of a soaring crime rate.
Supporters of the bill plan a rally Saturday evening in Tempe, just outside Phoenix, but the day belonged to tens of thousands of protesters, stretching two miles along a Phoenix street leading to the state Capitol.
Organizers said they expected 50,000 people. But Saturday morning, as people arrived at a Phoenix park for the start of the march, they said they may have underestimated.
Arizona resident Marlene Vazquez, 18, and her family came for the march, worried, they said, about how the bill would affect their own lives.
"There's no way that they're not going to racial profile," Vazquez told CNN affiliate KPNX in Phoenix. "How does someone look illegal?"
San Diego college professor Justin Akers Chacon told KPNX he and more than 100 others came to Phoenix Friday night, sleeping in a downtown warehouse that march organizers arranged for out-of-towners.
"There was a seriousness and confidence that we're all here for the right reasons," he told the station.
Chicagoan Eric Ruder, 40, said Arizona's law had captured the attention of the nation and many are very concerned.
"The criminalization of immigrants is a scary direction that this country is heading in," Ruder told another CNN affiliate in Phoenix, KNXV.
Supporters of the law, however, said opponents really didn't know what the law is about.
Phoenix resident David Kimball acknowledged that the bill's language isn't perfect, but said something had to be done.
"It's creating dialogue," he told KPNX. "Most protesters haven't read the bill. They don't have a clue."
Gina Loudon, an organizer of the pro-law rally Saturday night, dismissed the anti-law protest.
"Arizona has the right to enforce the laws that are already on the books," she told KNXV.
Critics and supporters agree on one point, however: The federal government has not done enough to curb illegal immigration.
Salvador Reza is an immigrant activist who opposes the law.
"Arizona has long been a testing ground of failed enforcement immigration polices ... that empower local authorities to racially profile and terrorize the community, all under the guise of federal immigration enforcement," said immigrant activist Salvador Reza. "The federal government helped create his disaster, now it must stop it."
The American Civil Liberties Union is leading a court challenge to the new law. Attorney General Eric Holder -- who this week met with a delegation of police chiefs from Arizona and elsewhere and dispatched key officials to meet with top Arizona officials to discuss the law -- has given no indication whether the federal government would file a legal challenge.
Meanwhile, Brewer released a statement saying she was bypassing Democratic Attorney General Terry Goddard and will rely on other lawyers to defend the state against challenges to the law. Goddard, who opposes the law and is running for governor against Brewer, said he would defend the law in court, but Brewer said the legislature had given her the power to use outside counsel "because of its lack of confidence in the Attorney General's willingness to vigorously defend" the law.