The U.S. Supreme Court agreed Monday to decide whether Republican lawmakers in North Carolina relied too heavily on race when they redrew the state's congressional districts in ways that gave the GOP a powerful advantage in the swing state.

The justices added the case to their calendar for the fall -- almost certainly too late to affect 2016's remaining races, But it could have an impact in the years ahead on partisan efforts to create electoral districts aimed at swaying the balance of power in Congress or in state legislatures.

North Carolina's GOP leaders deny factoring in race to an illegal extent, saying their 2011 map was designed primarily to give Republicans an edge and to comply with the federal Voting Rights Act.

Opponents argue that they unfairly stacked minorities into fewer districts after the 2010 Census in ways that diluted their influence.

A federal court ruled in February that race was the predominant factor in drawing two congressional districts, and ordered the state to quickly produce a new map for North Carolina's 13 members of Congress. That map was used in an unusual, separate, June 7 congressional primary.

The Supreme Court denied the state GOP's emergency request to intervene ahead of that primary, but key issues remain unresolved.

A ruling by the high court also is likely to heavily influence the outcome of a separate federal case challenging the districts used to elect North Carolina's state legislators.

North Carolina's status as a swing state belies the uneven split favoring Republicans in the state's legislature and congressional delegation. Narrowly contested presidential races in 2008 and 2012 show that voter preferences are split fairly evenly statewide.

But the GOP used redistricting in 2011 to create veto-proof majorities of more than two-thirds of the seats in the state legislature, and the state's congressional delegation now has 3 Democrats to 10 Republicans.

The case is McCrory v. Harris, 15-1262.