So far this year, Congress and the administration have made little progress in advancing immigration reform legislation, but Obama said Friday that if Congress failed to enact comprehensive reform, "We will continue to see misguided efforts opening up around the country."
The absence of a federal resolution of the controversial issue, he said, "opens the door to irresponsibility by others," and he cited "the recent efforts in Arizona, which threaten to undermine basic notions of fairness that we cherish as Americans."
The president has instructed the Justice Department to examine the Arizona law to see if it would violate civil rights. Other legal challenges are expected.
But even as the outcry continues, so does the applause from supporters of the law.
"Illegal is illegal," said Republican state Sen. Russell Pearce, who sponsored the bill. "We'll have less crime. We'll have lower taxes. We'll have safer neighborhoods. We'll have shorter lines in the emergency rooms. We'll have smaller classrooms."
Immigration reform has become a polarizing topic at all levels of government across the nation.
An estimated 12 million illegal immigrants live in the United States, and their presence is keenly felt in border states such as Arizona.
The Arizona law makes it a crime under state law to be in the U.S. illegally and allows police to arrest and question suspected undocumented persons about their status without a warrant. It also criminalizes the transporting of an illegal immigrant anywhere in the state, even if by a family member.
Brewer, who faces a tough Republican primary in August, signed the same bill that former Arizona Gov. Napolitano vetoed three times.
After the signing, crowds outside of the state capitol building erupted in anger. Carrying signs and American flags, they marched nearby, protesting the governor's decision.
Thousands of people wrote or called the governor's office, with a 10-to-one majority opposing the bill, a spokeswoman said.
"I don't think anything has been this extreme until this point," said Bridgette Gomez, a 24-year-old math tutor. "The evil is racial profiling, to think that you're going to always have to show identification. Because I'm tan, I must be illegal."
The Arizona bill takes effect in 90 days after the current legislative sessions over the next several weeks.
ABC News' Suzan Clarke and Kate McCarthy contributed to this report.