The case involved Section 5, which gives federal authorities open-ended oversight of states and localities with a history of voter discrimination. Any changes in voting laws and procedures in the covered areas -- which include all or parts of 15 states -- must be "pre-cleared" with Washington.
After the provision was reauthorized by Congress in 2006 for another 25 years, counties in Alabama and North Carolina filed suit, saying the monitoring was burdensome and unwarranted.
Civil rights groups say Section 5 has proved to be an important tool in protecting minority voters from local governments that would set unfair, shifting barriers to the polls. If it is ruled unconstitutional, they warn, the very power and effect of the entire Voting Rights Act would crumble.
But opponents of the provision counter that it should not be enforced in areas where it can be argued that racial discrimination no longer exists.