Story highlights Justices heard oral arguments in a Texas case challenging district lines based on population rather than eligible voters

Civil rights groups fear Latino communities in states with many nonvoting residents, as well as children and others, could be sharply disadvantaged

Washington (CNN) The Supreme Court grappled Tuesday with the "one person, one vote" doctrine in a case that could upend the way that states draw their legislative lines.

At issue is the principle dating back to the 1960s when the Supreme Court held that state legislative districts must be drawn so they are equal in population. Tuesday, justices dealt with something they've never explicitly answered: whether the doctrine applies to the general population or the voting population.

Civil rights groups are watching the case carefully, fearful that if the Court rules with the plaintiffs, it could potentially shift power from urban areas -- districts that tend to include a higher percentage of individuals not eligible to vote such as non-citizens, released felons and children -- to rural areas that are more likely to favor Republicans.

Justice Ruth Bader Ginsburg pointed out that most jurisdictions have used equal population to draw district boundaries. "So we have the states overwhelmingly -- for half a century -- using population as shown in the census, and now you're saying that they can't do that anymore," she asked lawyers for Sue Evenwel and Edward Pfenninger, two Texans who brought the challenge.

Edward Blum, the director of a conservative group called Project on Fair Representation, is backing the challenge. Blum's group was also behind a 2013 case that invalidated a central provision of the Voting Rights Act as well as a case this term seeking to strike down a race-conscious admissions program at the University of Texas. The plaintiffs argue that their vote is being diluted in relation to voters in other districts and that Texas must look primarily at the total number of eligible voters when it draws district lines.

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