[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/07/06/art.holder.doj.gi.jpg caption ="The Justice Department has filed a lawsuit challenging a contentious Arizona immigration law."]
Washington (CNN) - The Justice Department Tuesday filed a lawsuit challenging a tough new Arizona immigration law.
The law, which is scheduled to take effect at the end of July, requires immigrants to carry their alien registration documents at all times and allows police to question the residency status of people in the course of enforcing another law. It also targets businesses that hire illegal immigrant laborers or knowingly transports them.
President Barack Obama said in a speech July 1 that the measure has "fanned the flames of an already contentious debate." Among other things, it puts pressure on police officers to enforce rules that are "unenforceable" while making communities less safe - in part, by making people more reluctant to report crimes, he said.
It also has "the potential of violating the rights of innocent American citizens and legal residents, making them subject to possible stops or questioning because of what they look like or how they sound."
Before the government's filing, Arizona's two senators, both Republicans, called the Obama administration move "far too premature."
"Moreover, the American people must wonder whether the Obama administration is really committed to securing the border when it sues a state that is simply trying to protect its people by enforcing immigration law," Sens. Jon Kyl and John McCain said in a statement.
Democratic Rep. Ann Kirkpatrick called the suit a "sideshow" in a statement released before it was officially filed.
"A court battle between the federal government and Arizona will not move us closer to securing the border or fixing America's broken immigration system," she said.
Arizona's Republican governor, Jan Brewer, has accused the Obama administration of failing to secure the border with Mexico, thereby forcing her state to act on its own.
"Do your job. Secure the border," Brewer said of the president in a July 1 speech to a Republican group. She pledged to "defend this law against every assault, including attacks by the Obama administration."
Obama renewed his push for comprehensive immigration reform last week, calling for bipartisan cooperation on an issue reflecting deep social and political divisions.
Seeking an elusive middle ground on the subject, the president highlighted the importance of immigrants to American history and progress while acknowledging the fear and frustration many feel with a system that he said seems "fundamentally broken."
He asserted that the majority of Americans are ready to embrace reform legislation that would help resolve the status of an estimated 11 million illegal immigrants.
In his July 1 speech, Obama warned that rounding up everyone in the country who has entered illegally would be both "logistically impossible" and "tear at the fabric of the nation." At the same time, the president indicated it would be wrong to offer blanket amnesty for people who came into the United States unlawfully.
Despite Obama's call for bipartisan immigration reform, several senior Democratic sources said Thursday that they see virtually no chance of Congress taking up such a measure before November's midterm elections.
A CNN/Opinion Research Corp. national poll conducted in late May indicated that public support for beefing up security along the U.S. border with Mexico had grown significantly.
According to the survey, nearly nine out of 10 Americans want to increase U.S. law enforcement along the border with Mexico.
Eight in 10 questioned also supported a program that would allow illegal immigrants already in the United States to stay here and apply for legal residency, provided they had a job and paid back taxes.
But only 38 percent say that program should be a higher priority than border security and other get-tough proposals. Six in 10 said border security was the higher priority.
- CNN's Terry Frieden and Bill Mears contributed to this report