WASHINGTON, April 4 (Reuters) - The U.S. Supreme Court on Monday endorsed the way Texas draws its legislative districts based on total population and not just eligible voters - the same method used by all 50 states - rejecting a conservative challenge in a case focusing on the legal principle of "one person, one vote."
The eight-justice court unanimously rebuffed the challenge spearheaded by a conservative legal activist that could have shifted influence in state legislative races away from urban areas that tend to be racially diverse and favor Democrats to rural ones predominantly with white voters who often back Republicans.
Two of the court's conservatives, Clarence Thomas and Samuel Alito, concurred only in the judgment and did sign on to the opinion authored by liberal Justice Ruth Bader Ginsburg. The court is one justice short following the Feb. 13 death of conservative Justice Antonin Scalia, but the unanimous vote suggested his presence would not have substantially affected the outcome.
The court said Texas' method of drawing districts does not violate the long-established legal principle of "one person, one vote" endorsed by the Supreme Court in the 1960s during the era of the U.S. civil rights movement.
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Ginsburg wrote that the ruling was based on "constitutional history, the court's decisions and longstanding practice" that says states may draw legislative districts based on total population.
Adopting a new approach "would upset a well-functioning approach to districting that all 50 states and countless local jurisdictions have followed for decades, even centuries," Ginsburg wrote.
At issue in the case was whether equality of legislative representation necessitates equal numbers of all residents in voting districts regardless of whether they are eligible to vote or equal numbers of eligible voters.
The policy of counting all residents and not just those who are eligible voters boosts the electoral influence of locales, typically urban, with significant populations of people, often Hispanics, ineligible to vote, including legal and illegal immigrants as well as children.
Two Texas voters, Sue Evenwel and Edward Pfenninger, were recruited by conservative legal activist Edward Blum to file the lawsuit. Evenwel was a member of the Texas Republican Party's executive committee and Pfenninger worked as a security guard. Both lived in rural voting districts.
The challengers said the state Senate redistricting map signed into law by a Republican governor in 2013 failed to equally distribute voters, improperly expanding the voting power of urban areas. They asserted that the state's system violated the guarantee of equal protection under the law under the Constitution's 14th Amendment.
The dispute did not involve U.S. congressional districts. The Constitution requires seats in the U.S. House of Representatives to be distributed based on a state's total population, not just eligible voters.
The Obama administration supported the Texas plan.
Blum's group, the Project on Fair Representation, also orchestrated a lawsuit that in 2013 led the high court to invalidate a portion of the 1965 Voting Rights Act mandating federal approval for election law changes in states with histories of racial discrimination.
It also backed another important case heard by the Supreme Court in December, a white woman's challenge to a University of Texas admissions policy that considers an applicants' race among other factors in an effort to enroll more minority students. The court has not yet ruled in that case.
The case on which the court acted on Monday was Evenwel v. Abbott, U.S. Supreme Court, No. 14-940.