Tempe, Ariz. ? Thousands of people from around the country descended on the Phoenix area Saturday as supporters and opponents of Arizona’s tough new crackdown on illegal immigration held separate rallies.

Marchers carrying signs, banners and flags from the United States and Mexico filled a 5-mile stretch of central Phoenix, demanding that the federal government refuse to cooperate with Arizona authorities trying to enforce the law.

Police declined to estimate the size of the crowd, but it appeared at least 10,000 to 20,000 protesters braved 94-degree heat. Organizers had said they expected the demonstration to bring as many as 50,000 people.

Opponents of the law suspended their boycott against Arizona and bused in protesters from around the country. Some used umbrellas or cardboard signs to protect their faces from the sun. Volunteers handed out water bottles from the beds of pickup trucks, and organizers set up three water stations along the route.

The law’s opponents also gathered at capitols in states including Texas and Oregon, and about 300 people protested at the U.S. Embassy in Mexico City demanding legalization for undocumented Mexican workers in the United States.