"Almost all state and local efforts to address immigration outside the law in this generation have focused on areas of traditional state regulation, such as employment and housing," Motomura said. "SB 1070 much more clearly is a direct attempt to address and regulate immigration itself. This is why the federal government had to take action in this case, in order to maintain its constitutional position as the exclusive authority on who is let into the United States, who must leave, and ultimately, who is or can become an American."
Meanwhile, law enforcement officers across Arizona are preparing to enforce the measures not blocked Wednesday.
"We're not engaged in [racial profiling] now in all types of crimes we enforce. So what's the difference whether you enforce another crime, which is the illegal immigration? So we are very comfortable" enforcing the law, Maricopa County Sheriff Joe Arpaio said on "Good Morning America."
Many immigrant families have begun fleeing the state afraid of the new law's impact, and some activists are even encouraging immigrants to check tail lights on their cars, not to travel in large groups, and remove the Catholic rosaries from their rear-view mirrors.
Erika, a 23-year-old undocumented Mexican student living in Mesa, Ariz., since 1998, says her family is relieved with Wednesday's court ruling.
"Yesterday I went to bed really depressed," she said. "This morning, knowing this, everything came back. The hope, the faith, knowing that those prayers are really working."
"This means the community won't be as afraid to go with their friends, go out to the store," said Nicole Torres, who was participating at church vigil outside Phoenix after the ruling. "They hopefully will still feel safe enough to call the police now that they will no longer require you know checking of documentation."
Rosario Peralta, a legal immigrant who runs a south Phoenix grocery store, said some of the frightened families that had planned to move out of the state appear to be rethinking their decisions.
"I was worried about my customers...business was slow, but it's going to get better," she said.
The Arizona immigration law, which passed in late April, has attracted international attention and sparked protests around the country. It faces legal challenges in six lawsuits, in addition to the one filed by DOJ.
Sixty percent of Americans support the Arizona law, according to the most recent ABC News/Washington Post poll. But fewer -- 46 percent -- think the states should have power to make and enforce their own immigration laws, one criticism of the Arizona statute.
ABC News' Lauren Pearle, Jessica Hopper, Barbara Pinto and Julie Percha contributed to this report.