In a series of cases following the 1990’s redistricting, the United States Supreme Court declared unconstitutional a number of Congressional districts in North Carolina, Georgia and Texas. The Court declared that the districts in question were created predominantly for racial reasons and, therefore, were unconstitutional under Section 1 of the Fourteenth Amendment (equal protection clause). In holding the districts unconstitutional, the Court noted that bizarrely-shaped districts, and those which do not follow traditional districting principles such as compactness, contiguousness, communities of interest and political boundaries, are unconstitutional if drawn for the purpose of favoring one race over another, unless there is a compelling state interest in doing so. The Supreme Court has held that avoiding a violation of Section 2 of the Voting Rights Act of 1965 provides such a compelling reason to draw race-based districts. Other possible exceptions might be avoiding a violation of Section 5 of the Voting Rights Act and to remedy past discrimination.
Reference: The Fourteenth Amendment
In Gomillion v. Lightfoot, 364 U.S. 339 (1960), The United States Supreme Court held that it was unlawful to purposefully exclude African-American voters from voting districts under the Fifteenth Amendment to the United States Constitution, which states:
Reference: The Fifteenth Amendment