The U.S. Supreme Court has voided a key part of the Voting Rights Act of 1965 that subjects several states to federal oversight.
Justices ruled 5 to 4 Tuesday that the landmark provision cannot be enforced unless Congress establishes a new formula determining which states should require close federal election monitoring.
They argue the law relies on 40-year-old data that doesn't reflect racial progress.
"In 1965, the states could be divided into two groups: those with a recent history of voting tests and low voter registration and turnout, and those without those characteristics," Chief Justice John Roberts wrote for the majority.
"Congress based its coverage formula on that distinction," he said. "Today the nation is no longer divided along those lines, yet the Voting Rights Act continues to treat it as if it were."
The court decided to keep part of the law enacted in the 1960s that opened up polling places to minority voters.
Liberals complain the decision guts one of the nation's most important civil rights laws.