Washington (CNN) -- The Obama administration has formally asked a federal appeals court in Atlanta to rule in favor of the sweeping health care reform law.

The Justice Department filed its brief Sunday with the U.S. Court of Appeals for the 11th Circuit over a key provision of the law requiring most Americans to obtain health insurance or face severe financial penalties.

A federal judge in Florida had ruled that part of the law unconstitutional on January 31, setting up the current appeal. A three-judge panel of the 11th Circuit will hear oral arguments in the case in June.

Florida and more than two dozen states have banded together to launch a high-stakes legal challenge to the law, a signature accomplishment of President Barack Obama's first term.

Similar appeals have been filed by other states and private groups. A federal appeals court in Richmond will hear a challenge from Virginia in May. The issue is almost certain to reach the Supreme Court, perhaps by year's end.

The current case is Florida v. U.S. Department of Health and Human Services (11-11021).