The United States Supreme Court has struck down part of a civil rights-era electoral law designed to protect minority voters.
By a margin of 5-4, the justices quashed section 4 of the 1965 Voting Rights Act.
They ruled that an updated formula was needed to decide which jurisdictions' election laws need monitoring.
The law requires all or parts of 15 US states, mostly in the South, to receive federal approval for election changes.
The Voting Rights Act was extended for 25 years by Congress in 2006 with broad support.
"Congress did not use the record it compiled to shape a coverage formula grounded in current conditions," wrote Chief Justice John Roberts.
"It instead re-enacted a formula based on 40-year-old facts having no logical relationship to the present day."
The BBC reports the ruling effectively renders section 5 invalid until a new formula can be agreed by Congress.
The case was brought by Shelby County, Alabama, which argued that the pre-clearance process was out of date and an over-reach of federal power.
The Voting Rights Act was intended to stop practices such as literacy tests, poll taxes or similar measures to keep black people from voting