The Supreme Court will decide the constitutionality of a federal law that permits sex offenders to be kept behind bars after they complete their prison terms.

The justices, acting Monday, say they will consider the Obama administration's appeal of a lower court ruling that invalidated the law.

The 4th U.S. Circuit Court of Appeals in Richmond, Va., ruled in January that Congress overstepped its authority when it enacted a law allowing for indefinite commitment of people who are considered "sexually dangerous."

In April, Chief Justice John Roberts granted an administration request to block the release of up to 77 inmates at a federal prison in North Carolina. These were people whose prison terms for sex offenses were ending. The justice's order was designed to allow time for the high court to consider the administration's appeal.

The challenge to the law was brought by four men who served prison terms ranging from three to eight years for possession of child pornography or sexual abuse of a minor. Their confinement was supposed to end more than two years ago, but the government determined that there would be a risk of sexually violent conduct or child molestation if they were released.

A fifth man who also was part of the legal challenge was charged with child sex abuse, but declared incompetent to stand trial.