The Supreme Court will review a districting plan for the Virginia House of Delegates that challengers say gives too little power to African-American voters in an effort to boost Republican strength.

The justices on Monday added the Virginia case to their docket for the fall.

The case concerns claims that black voters were illegally packed into a dozen legislative districts. The challengers say the plan made neighboring districts safer for Republicans because those districts had fewer black voters, who tend to support Democrats.

The court last month dismissed a Republican-led appeal that sought to preserve a congressional districting map that similarly concentrated black voters in one district and improved GOP prospects elsewhere in the state.

In the new case, a panel of three federal judges had voted 2-1 to uphold 11 of 12 districts. The court said that the challengers had failed to prove that race was the predominant factor in the composition of the districts. The dissenting judge said Virginia's General Assembly had applied a "one-size-fits-all racial quota" to 12 dissimilar districts.

The case is Bethune-Hill v. Virginia State Board of Elections, 15-680.