The justices are hearing arguments Monday in redistricting disputes from North Carolina and Virginia.
The claim made by black voters in both states is that Republicans created districts with more reliably Democratic black voters than necessary to elect their preferred candidates, making neighboring districts whiter and more Republican.
A federal court struck down two North Carolina districts as unconstitutional because they relied too heavily on race. In Virginia, a court rejected a constitutional challenge to 12 state legislative districts.
The justices have frequently considered the intersection of race and politics. In 2015, Justice Anthony Kennedy joined the four more liberal justices to order a review of Alabama legislative districts. Justice Stephen Breyer wrote for the court that the Alabama legislature and the federal court that ruled on the plan had taken a "mechanically numerical" view, instead of trying to figure out what percentage of black voters were needed to elect a candidate of their choice.
In 2013, Kennedy sided with more conservative justices to effectively block a key component of the landmark Voting Rights Act that led to the election of African-Americans across the South. Its provisions requiring states to create and preserve districts in which minority voting groups can elect their candidate of choice remain in effect.
North Carolina and Virginia argue that they were trying to preserve majority-black districts. In Virginia, lawmakers made sure that at least 55 percent of the eligible voting-age population in each district was African-American. Redistricting follows the once-a-decade census, when population changes require the adjustment of political districts.
In North Carolina, the federal court also struck down some state House and Senate districts, and last week, those judges ordered new districts drawn and special elections held next year.
North Carolina Republicans have used the current districts to achieve veto-proof majorities in both chambers. In addition, they hold 10 of the state's 13 congressional seats. By contrast, statewide contests suggest a narrower gap between the parties. Two Republicans won statewide elections last month, President-elect Donald Trump with just under 50 percent of the vote and Sen. Richard Burr, with 51 percent. Republican Gov. Pat McCrory trails in his not-yet-decided re-election bid.
The cases are Bethune-Hill v. Virginia State Board of Elections, 15-680, and McCrory v. Harris, 15-1262.
Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.