The federal government asked an appeals court on Friday to halt an Alabama immigration law considered by many as the toughest in the United States, saying it invites discrimination against foreign-born citizens and legal immigrants.

The federal government filed the challenge to the 11th Circuit Court of Appeals in Atlanta. It claimed Alabama's new law "is highly likely to expose persons lawfully in the United States, including school children, to new difficulties in routine dealings."

The overhaul allows authorities to question people suspected of being in the country illegally and hold them without bond. It also lets officials check the immigration status of students in public schools.

A federal judge in Alabama upheld those two key aspects of the law, which have already taken effect.

Those provisions that took effect are what help make the Alabama law stricter than similar laws passed in Arizona, Utah, Indiana and Georgia. Other federal judges have blocked all or parts of the laws in those states.

Immigration became a hot issue in Alabama over the past decade as the state's Hispanic population grew by 145 percent to about 185,600. While the group still represents only about 4 percent of the population, some counties in north Alabama have large Spanish-speaking communities and schools where most of the students are Hispanic...