*Editor's note: This story has been updated throughout.

The U.S. Supreme Court agreed Tuesday to hear a case that centers on how Texas draws its political districts, a longtime point of dispute between the state and voting rights advocates.

The high court said it will take up Evenwel v. Abbott, which involves whether Texas should use total population or voting age population when composing districts. The debate is especially pertinent in Texas, where some districts include many people living in the country illegally who are not eligible to vote. 

A few years ago, two voters challenged the constitutionality of Texas' state Senate maps, claiming they violated the Supreme Court's previously established principle of "one person, one vote." The voters,  Sue Evenwel and Edward Pfenninger, are supported by the Austin-based Project on Fair Representation. 

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At the heart of their argument is the disparity between the number of eligible voters in rural and urban areas. For example, the project has noted that Evenwel comes from a mostly rural district with about 584,000 voters, while an adjacent, mostly urban district has just 372,000. The difference, according to the plaintiffs, means the urban voters have more influence.

The justices' 1964 ruling in Reynolds v. Sims held that state legislative districts have to be about equal in population, but it remains unsettled how the high court defines population. Evenwel and Pfenninger are seeking to show voting age population, not total population, is more congruent with the Supreme Court's idea of "one person, one vote." 

Former Gov. Rick Perry signed the Senate boundaries into law in 2013. Since then, civil rights group have challenged them and other Texas redistricting maps in federal court, arguing they discriminate against minorities. 

The Project on Fair Representation, which is helping the plaintiffs in Evenwel v. Abbott, has a history of fighting race-based rules, including a former applicant's challenge to the University of Texas at Austin's affirmative action policies. In a statement Wednesday, Edward Blum, the head of the group, said the redistricting case "presents the Court with the opportunity to restore the important principle of one-person, one-vote to the citizens of Texas and elsewhere."

The group's critics contend its intentions are more malicious. State Sen. José Rodríguez, who chairs the Senate Hispanic Caucus, said Tuesday that the project is "seeking to undermine minority representation in the Texas Senate by claiming that not all people living the district should be counted." In a statement, the El Paso Democrat called the group's challenge a "frivolous case."

The Supreme Court agreed to take up Evenwel v. Abbott for its next term, which begins in October. 

Disclosure: The University of Texas at Austin is a corporate sponsor of The Texas Tribune. A complete list of Tribune donors and sponsors can be viewed here.

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