Thousands of mostly Hispanic immigrants will march in US cities Saturday to press for immigration reform and condemn Arizona's controversial new immigration law, organizers said. "It's important we unite and take part in a peaceful march to demand respect for our community's rights and dignity," said Eddie "Piolin" Sotelo, America's top Hispanic radio commentator. Organizers on Thursday said thousands of people will take part in marches in 70 US cities, with Los Angeles staging one of the biggest that will include musician and other top-rated Hispanic entertainers. Under the slogan "Todos Somos Arizona" (We are all Arizona), the demonstrations will focus opposition against recently passed legislation to curb illegal immigration in the southwestern state, which critics say enshrines racial profiling. The law, signed by Arizona's Republican Governor Jan Brewer last Friday, allows police to question anyone they believe may be an illegal immigrant, even if they are not suspected of committing a crime. After it unleashed anger on both sides of the US-Mexican border, the law already faces threats of court challenges as the state confronts a national campaign to boycott its exports and tourism industry. Los Angeles Mayor Antonio Villaraigosa, who is of Mexican origin, said he backs a proposal by two city officials to implement a city-wide economic boycott of Arizona to prevent the new law from being implemented. The American Civil Liberties Union, the Mexican American Legal Defense and Educational Fund (MALDEF) and the National Immigration Law Center announced a legal challenge to the new law Thursday in front of Arizona's state capitol. MALDEF president Thomas Saenz told a news conference "a vigorous and sophisticated" legal challenge would seek to "prevent this unconstitutional and discriminatory law from ever taking effect." President Barack Obama has also weighed into the debate, describing the Arizona legislation as "polarizing." US Senate Democrats unveiled Thursday a plan to give the nation's undocumented workers a long, winding path to citizenship. But few analysts predict Congress will pass an immigration overhaul ahead of November mid-term elections, with US unemployment near 10 percent, and anger at an estimated 10.8 million undocumented immigrants in a nation of 309 million people. A poll published by the Angus Reid Global Monitor group Thursday reported that roughly 71 percent of 1,002 American adults polled backed the Arizona law. National Day Laborer Organization Network director and May 1 demonstration organizer Pablo Alvarado told AFP there will be substantial participation in the marches. "We've decided to gather in Los Angeles the greatest number of immigrant rights activists, while in Arizona we'll undertake a day-long education campaign on the new law and the rights of our community," added the Arizona resident.