Washington (CNN) -- A deeply divided Supreme Court has limited use of a key provision in the landmark Voting Rights Act of 1965, in effect invalidating federal enforcement over all or parts of 15 states with past history of voter discrimination.
The court said it is now up to congressional lawmakers to revise the law to meet constitutional scrutiny.
"Our country has changed, and while any racial discrimination in voting is too much, Congress must ensure that the legislation it passes to remedy that problem speaks to the current conditions," said Chief Justice John Roberts for the 5-4 conservative majority.
Section 4 of the law was struck down, the coverage formula used by the federal government to determine which states and counties are subject to continued oversight. Roberts said that formula from 1972 was outdated and unworkable.
The practical impact of the majority ruling means the separate Section 5-- the key enforcement provision-- cannot be enforced.
Any changes in voting laws and procedures in those covered states-- including much of the South-- must be "pre-cleared" with Washington. That could include something as simple as moving a polling place temporarily across the street.
The two key provisions were reauthorized by Congress in 2006 for another 25 years and officials in Shelby County, Alabama, subsequently filed suit, saying the monitoring was overly burdensome and unwarranted.
"Congress could have updated the coverage formula at that time, but did not do so," said Roberts. "Its failure leaves us today with no choice but to declare Section 4 unconstitutional. The formula in that section can no longer be used as a basis for subjecting jurisdictions to preclearance."
The case is Shelby County, AL v. Holder (12-96).