More than 1 million undocumented young people, most of them of Mexican or Latin American origin, became eligible on Wednesday for a program that would protect them from deportation and give them a legal right to work in the United States.
The Deferred Action initiative was announced by President Barack Obama on June 15.
Coming a few months before the Nov. 6 elections, the move has been denounced by the president's Republican opponents as political opportunism.
Pro-immigrant groups, however, call it a historic moment.
The last time the U.S. government granted relief on this scale to undocumented immigrants was in 1986, when 3 million people received permanent residence under a broad amnesty.
To mark the program's official launch, organizations scheduled events Wednesday in states with large immigrant populations, including California, Texas, Illinois, Florida and New York.
Community centers nationwide are offering free legal advice to prospective applicants, known as "Dreamers" because the Deferred Action program is aimed at the same young immigrants who would benefit if Congress passed the DREAM Act.
U.S. Citizenship and Immigration Services says Deferred Action does not represent a path to permanent residence, only a renewable two-year guarantee of no deportation and the opportunity to obtain a work permit and a driver's license.
The Deferred Action program is open to undocumented immigrants 30 years old and younger who were brought to the United States before the age of 16.
Applicants will need five years of continuous residence in the country, a high school diploma or GED, and proof of current or previous military service or college enrollment.
Those seeking deferred action will also have to submit fingerprints and other biometric data and undergo an extensive background check, as well as pay a fee of $465.
The cases of applicants rejected on the basis of a criminal record, or for lying on their applications, will be referred to Immigration and Customs Enforcement, USCIS said.
Most immigration reform activists see Deferred Action as a good first step while the country waits for Congress to devise a permanent solution for the estimated 11 million undocumented immigrants in the United States.
Republicans accuse Obama of seeking to distract Hispanics from his failure to deliver the immigration reform he promised in the 2008 campaign.
While both parties are actively courting Latinos, polls show the Democratic incumbent leads presumptive Republican nominee Mitt Romney among Hispanics by 67 percent to 23 percent.
Romney has promised to push immigration reform if he reaches the White House, but said during the GOP primaries that he would veto the DREAM Act.
Think-tank estimates of the number of potential beneficiaries of Deferred Action range from 1.39 million to 1.76 million. EFE