Agreeing to hear another important case on race in America, the Supreme Court said Friday it will take up a battle over a key part of the landmark Voting Rights Act. Civil rights groups fear the court will use this case to gut the law.

Passed by Congress in 1965 and renewed four times since then, most recently in 2006, a key provision requires states with a history of discrimination at the polls to get federal permission before making any changes to election procedures -- from redrawing congressional district boundaries to changing the locations of polling places.

The law was at the core of the legal cases this year blocking strict new voter ID laws in Texas and South Carolina.

Shelby County, Ala., claims the pre-clearance requirement -- which currently covers nine entire states, 12 cities and 57 counties elsewhere -- is unconstitutional. Under the law, those states and areas are presumed to be acting improperly whenever they seek election changes and "must either go hat in hand to Justice Department officialdom to seek approval, or embark on expensive litigation in a remote judicial venue," says the lawyer for the county.

The areas covered by the law, Shelby County says, include some localities that have made substantial reforms while missing other parts of the country that have failed to root out discrimination at the polls.  "Florida has been forced into pre-clearance litigation to prove that reducing early voting from 14 days to 8 is not discriminatory, when states such as Connecticut, Rhode Island, and Pennsylvania have no early voting at all," the county says.

But the NAACP Legal Defense and Education Fund says the current map is a close enough fit to cover the areas of greatest concern.  "Congress is not a surgeon with a scalpel when it acts to legislate across the 50 states. But it can reasonably attack discrimination where it finds it," the group says.

Three years ago, the Supreme Court narrowly rejected a challenge to the pre-clearance  requirement but strongly suggested that several justices had doubts about its constitutionality, given recent electoral reforms. "Things have changed in the South," the court said in 2009.  "Blatantly discriminatory evasions of federal decrees are rare."

Last month, the Supreme Court heard another racially charged case, re-examining whether the nation's colleges can use affirmative action in admissions.