WASHINGTON (AP) — The Supreme Court limited the reach of the Voting Rights Act on Monday, a decision that could make it harder for some minority candidates to win election when voting districts are redrawn.

In a 5-4 decision, the justices ruled that a portion of the law aimed at helping minorities elect their preferred candidates only applies in districts where minorities make up more than half the population.

The decision could make it more difficult for Democrats, particularly in the South and Southwest, to draw electoral boundaries friendly to black or Hispanic candidates following the 2010 Census.

The Mexican American Legal Defense and Educational Fund said the decision weakens minorities’ ability to use the Voting Rights Act to challenge alleged discrimination in electoral districts.

“The Supreme Court decision, if left unchecked, will make redistricting in 2011 and the cause of making districts reflect emerging Latino electoral strength much harder,” said Nancy Ramirez, MALDEF’s western regional counsel.

With the court’s conservatives in the majority, the court ruled that North Carolina erred when trying to preserve the influence of African-American voters even though they made up just 39 percent of the population in a state legislative district.

While not a majority, the black voters were numerous enough to effectively determine the outcome of elections, the state argued in urging the court to extend the civil rights law’s provision to the district.

The state said the district should be protected by the section of the law that bars states from reducing the chance for minorities to “elect representatives of their choice.”

Justice Anthony Kennedy, announcing the court’s judgment, said the court had never extended the law to those so-called crossover districts and would not do so now. The 50 percent rule “draws clear lines for courts and legislatures alike,” Kennedy said in ruling against the North Carolina district.

In 2007, the North Carolina Supreme Court had struck down the district, saying the Voting Rights Act applies only to districts with a numerical majority of minority voters. The district also violated a provision of the state constitution keeping district boundaries from crossing county lines, the court said.

Kennedy said that, absent prohibitions like North Carolina’s rule against crossing county lines, “states that wish to draw crossover districts are free to do so.” But they are not required, he said.

Chief Justice John Roberts and Justice Samuel Alito signed onto Kennedy’s opinion. Justices Antonin Scalia and Clarence Thomas agreed with the outcome of the case.

The four liberal justices dissented. A district like the one in North Carolina should be protected by federal law “so long as a cohesive minority population is large enough to elect its chosen candidate when combined with a reliable number of crossover voters from an otherwise polarized majority,” Justice David Souter wrote for himself and Justices Stephen Breyer, Ruth Bader Ginsburg and John Paul Stevens.

Ginsburg also suggested that Congress could amend the law to cover districts like the one in North Carolina.

Civil rights groups that urged the court to uphold the North Carolina plan said such districts help to diminish racially polarized voting over time because the candidate who is the choice of black or Hispanic voters must draw some white support to win election.

In April, the court will hear a more significant challenge to another provision of the Voting Rights Act, requiring all or parts of 16 states with a history of racial discrimination to get approval before implementing any changes in how elections are held.

The court’s familiar ideological split in this case strongly suggests that Kennedy could hold the key to the outcome in the April case as well, said Nathaniel Persily, an election law expert at Columbia University.

In another election-related case, the court let stand an appeals court decision that invalidated state laws regulating the ways independent presidential candidates can get on state ballots.

Arizona, joined by 13 other states, asked the court to hear its challenge to a ruling throwing out its residency requirement for petition circulators and a June deadline for submitting signatures for independent candidates in the November presidential elections.

Independent presidential candidate Ralph Nader sued and won a favorable ruling from the 9th U.S. Circuit Court of Appeals in San Francisco.

The cases are Bartlett v. Strickland, 07-689, and Brewer v. Nader, 08-648.

On Monday, the Supreme Court:

  • Ruled that electoral districts must have a majority of African-Americans or other minorities to be protected by a provision of the Voting Rights Act. The court declined to expand protections of the landmark civil rights law to take in electoral districts where the minority population is less than 50 percent of the total, but strong enough to effectively determine the outcome of elections.
  • Let stand a lower court decision that invalidated Arizona’s laws requiring presidential petition circulators to be residents and setting a June deadline for submitting signatures for independent candidates in the November presidential elections.
  • Ruled that a state is not responsible for a public defender’s delays in bringing a criminal case to trial. A lower court had said Michael Brillon’s right to a speedy trial was violated after he was jailed for three years and went through six defense attorneys before his trial.
  • Rejected claims by Kansas that it is owed $9 million in legal fees from Colorado due to their centurylong dispute over water rights to the Arkansas River.
  • Refused to revive lawsuits by New York City and gun violence victims that would hold the firearms industry responsible for selling guns that could end up in illegal markets.
  • Refused to consider whether the mother of a Texas A&M student injured in a deadly bonfire collapse nearly a decade ago can sue because of the damage to her relationship with her son.
  • Decided that consumers can sometimes resist credit card companies’ push to move their dispute over finance charges and late fees to arbitration instead of the courts.
  • Refused to get involved in a patent dispute between Star Scientific, Inc., and R.J. Reynolds Tobacco Co. over a way to cure tobacco that may make it less carcinogenic.
  • Refused to allow InfoSpace founder Naveen Jain to sue a stock management company and his former lawyers for allegedly bungling an insider stock trading case that resulted in a $247 million judgment against him.