The Virginia Supreme Court blocked a new Democratic-drawn congressional map from taking effect, delivering a major boost for Republicans as they defend their narrow House majority in the midterm elections.

Weeks after voters narrowly approved the plan in a statewide referendum, the court ruled that Democratic lawmakers did not meet the procedural requirements to place a constitutional amendment on the ballot, which was written to pave the way for the redrawn district lines. Democrats were seeking a map designed to give the party up to four new House seats.