Attorneys defending the Virginia voter-approved redistricting ballot amendment faced sustained — and, at times, skeptical — questioning Monday from the Supreme Court of Virginia, as justices weighed whether to invalidate the measure over alleged procedural violations.

The case centers on a Republican-led challenge arguing that the Democrat-controlled General Assembly failed to follow the strict constitutional process required to place a redistricting amendment before voters. If the court agrees, it could nullify last week’s narrowly approved statewide vote and upend newly drawn congressional districts that Democrats hope will net them several additional House seats.