Missouri's Supreme Court has blocked the use of a new congressional map, ruling that voters must approve the district lines in a statewide referendum before they can take effect. The decision, which came on Wednesday, prevents election officials from using the map in upcoming primaries. The map, drawn by Republican lawmakers, was challenged by Democrats who argued it diluted minority voting strength.

The court's ruling orders a lower court to determine if the map complies with the state constitution, which requires districts to be "contiguous and compact." This setback could delay primary elections, which are scheduled for August, unless the legislature acts quickly to redraw the map or the court allows an emergency solution. The decision is a victory for voting rights advocates, who see it as a check on partisan gerrymandering.