Split along ideological and partisan lines, the justices voted 5-4 Tuesday to halt enforcement of the requirement in the Voting Rights Act that all or parts of 15 states with a history of discrimination in voting get Washington's approval before changing the way they hold elections.
The Voting Rights Act was an emergency federal measure in 1965 — a turbulent time when it was not unusual for blacks to essentially be barred from voting in some parts of the country, and some civil rights activists on the issue were killed. The act was just one instance of the federal government stepping in during that era to make local governments obey the law and ensure equal rights for all.
Tuesday's ruling, led by Chief Justice John Roberts writing for a conservative majority, was the most dramatic decision so far as the high court re-examines the necessity of laws and programs aimed at giving racial minorities access to areas from which they once were systematically excluded.
The U.S. racial landscape is rapidly changing. Census estimates look ahead to whites becoming a minority in coming decades.
In his majority decision, Roberts said the law's provision that determines which states are covered is unconstitutional because it relies on 40-year-old data and does not account for racial progress and other changes in U.S. society.
The decision effectively puts an end to the advance approval requirement that has been used to open up polling places to minority voters in the nearly half century since it was first enacted in 1965, unless Congress can come up with a new formula that Roberts said meets "current conditions" in the United States. That seems unlikely to happen any time soon.
Rights groups and the court's dissenting liberal justices warned that discrimination still exists.
Justice Ruth Bader Ginsburg, dissenting from the ruling along with the court's three other liberals, said there was no mistaking the court's action.
"Hubris is a fit word for today's demolition" of the law, she said.
Jon Greenbaum, chief counsel for the Lawyers' Committee for Civil Rights Under Law, said the Supreme Court "has effectively gutted one of the nation's most important and effective civil rights laws."
" Minority voters in places with a record of discrimination are now at greater risk of being disenfranchised than they have been in decades," he said.
Obama, re-elected last year with the strong support of black and Hispanic voters, called on Congress to reinvigorate the voting rights law.
"While today's decision is a setback, it doesn't represent the end of our efforts to end voting discrimination," the president said. "I am calling on Congress to pass legislation to ensure every American has equal access to the polls."
The requirement for federal approval for proposed election changes was put into the law to give federal officials a potent tool to defeat persistent efforts to keep blacks from voting. But coverage also has been triggered by past discrimination against American Indians, Asian-Americans, Alaska Natives and Hispanics.
The requirement currently applies to the states of Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. It also covers certain counties in California, Florida, New York, North Carolina and South Dakota, and some local jurisdictions in Michigan.
Alabama Gov. Robert Bentley said that, while the requirement was necessary in the 1960s, that was no longer the case. He said, "We have long lived up to what happened then, and we have made sure it's not going to happen again."
Bentley, a Republican, pointed to his state's legislature — 27 per cent black, similar to Alabama's overall population — as a sign of the state's progress.
Tuesday's ruling came in a challenge brought by Shelby County, Alabama, a suburb of Birmingham — one of the Southern cities where the civil rights struggle played out in the 1960s.
The lawsuit acknowledged that the measure had been appropriate and necessary to counteract decades of state-sponsored discrimination in voting, but it asked whether there was any end in sight for a provision that intrudes on states' rights to conduct elections.
Rep. Bennie Thompson, the only black lawmaker in Mississippi's congressional delegation, said the ruling "guts the most critical portion of the most important civil rights legislation of our time."
Tuesday's decision means that a host of state and local laws that have not received Justice Department approval or have not yet been submitted can take effect. Prominent among those are laws in Alabama and Mississippi requiring voters to show government-issued photo identification. Democratic-leaning groups — such as the poor, minorities, and students — are less likely to have such identification.
Texas Attorney General Greg Abbott, a Republican, said his state's voter ID law, which a panel of federal judges blocked as discriminatory, also would be allowed to take effect.
Associated Press writer Mark Sherman contributed to this report.