"In its 4-to-3 opinion, the Virginia Supreme Court wrote that Democratic legislators had violated the state’s constitution with their move to enact a new map meant to give their party 10 out of the state’s 11 U.S. House seats..."

".... up from the six it currently controls. Virginia voters had approved a constitutional amendment to allow for the map in a referendum. The problem, the court’s majority suggested, was that the first vote on the amendment in the General Assembly, which would authorize Democrats to redraw the map, occurred days before last fall’s legislative elections — meaning that some Virginians who cast their ballots early did so without knowing how their state lawmakers would vote on the new map. That, the justices wrote, violated the process laid out in the State Constitution. 'This constitutional violation incurably taints the resulting referendum vote and nullifies its legal efficacy,' the majority wrote...."

I'm reading "In Huge Blow to Democrats, Virginia Court Strikes Down House Map/The decision is a major victory for Republicans, wiping away a measure approved by voters to allow Democrats to gain as many as four House seats in the midterms" (NYT).

Democrats seemed despondent over the decision; they had invested eight months and nearly $70 million to pass the referendum.... Some legal experts believe that the Virginia Supreme Court’s ruling may be the final word on the state’s maps before the election. That is because the case involved a challenge to a state law about whether lawmakers had followed rules laid out in the Virginia Constitution, not a question of federal law or the U.S. Constitution...."

If it's a state law question, the state supreme court is the final word.

In the lawsuits, Republicans argued that the language in the amendment was misleading, that the new districts were not drawn compactly, that it was improper to vote on redistricting at a legislative session that had convened to discuss budget issues and that a state law would have required county clerks to post notices about the amendment months before it was actually voted on. One of the most critical questions was about the sequence of events in Virginia’s complex amendment process. Before voters weigh in on an amendment to the State Constitution, the General Assembly must approve it twice, with an election for the state’s House of Delegates taking place between the two votes. The first vote for this amendment was on Oct. 31, just days before the state election. With hundreds of thousands of Virginians having already voted, Republicans argued that the legislative action had come too late. The court sided with that argument. “Early Virginia voters unknowingly forfeited their constitutionally protected opportunity to vote for or against delegates who favor or disfavor amending the Constitution by not anticipating a legislative vote on a constitutional amendment four days before the last day of voting,” the court’s majority wrote.

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Here's my post from April 22d about the referendum, which stressed the problem with the misleading wording. That wasn't the basis of the decision, which was about the procedure for putting an constitutional amendment on the ballot.