The Supreme Court has decided to take up a “one person, one vote” case originating from Texas, which uses total population, as opposed to number of eligible voters, in drawing its districts. (Karen Bleier/AFP/Getty Images)

Decades after the Supreme Court set “one person, one vote” as the standard states must meet in creating legislative districts that equitably distribute political power, the justices agreed Tuesday to decide exactly which persons should count.

The court, in accepting a Texas case brought by a conservative advocacy group, will consider whether states and localities may continue to use a place’s total population as the basis or must make redistricting decisions based on the number of citizens who are eligible to vote.

A shift from using total population would have an enormous impact in states with large immigrant populations because of the greater numbers of children and noncitizens. It would most likely transfer power from urban areas to more rural districts. The court will schedule the case for the new term that begins in October.

In 1964, the Supreme Court ruled that states must draw electoral districts based on population so that political power is equally shared. The justices did not specify the method states should use, but lower courts have never found that any state violated the Constitution by using the total population.

“Plaintiffs cite no case in which a court has accepted their claim that the Constitution compels states to apportion their legislative districts based on voter population as opposed to or in addition to total population,” Texas Attorney General Ken Paxton (R) wrote in trying to dissuade justices from accepting the case. “And multiple precedents from this court confirm that total population is a permissible apportionment base under the Equal Protection Clause.”

The challenge is brought by the Project on Fair Representation, an organization headed by Edward Blum that opposes racial and ethnic classifications. It has been successful in recent years in getting the court’s attention with challenges to affirmative action in higher education and to the federal Voting Rights Act.

The challengers are Sue Evenwel and Edward Pfenninger, who live in Texas Senate districts that are similar to others in total population but not in the number of eligible voters. This dilutes the value of their individual votes, they allege.

“This case presents the court with the opportunity to restore the important principle of one-person, one-vote to the citizens of Texas and elsewhere,” Blum said in a statement.

A three-judge federal panel ruled against the challengers, saying that their theory had never been accepted by the Supreme Court and that the method of reapportionment was “unambiguously left to the states” so long as it did not harm certain groups.

Election law experts were somewhat surprised by the court’s decision to take the case, given the lack of disagreement in lower courts. Still, all acknowledge it is a question the Supreme Court has left unanswered for decades.

There is “something odd,” said Richard Pildes, a law professor at New York University, “about the principle of political equality that’s reflected in the ‘one person, one vote’ standard being so ill-defined” that it is left up to states to choose the method. “Few constitutional standards work that way.”

But only Justice Clarence Thomas objected in 2001 when the court passed on another case that called for setting a standard. “As long as we sustain the one-person, one-vote principle, we have an obligation to explain to states and localities what it actually means,” Thomas wrote.

The challengers contend the principle refers to voting, and protecting the individual right, rather than representation, which would take in the total population. Besides, they contend, there was a way for Texas to draw the lines to do both.

Some experts noted practical problems in the challengers’ approach. States are redistricted after the every-decade census. But that count does not provide estimates for citizen voting age populations; those are done in different surveys.

“The Constitution only requires a census of the population, not the survey products that produce interesting statistics like citizenship,” said Michael P. McDonald, an elections expert at the University of Florida.

He added: “I can easily imagine a war of experts over how to construct citizenship estimates.”

The case is Evenwel v. Abbot t.

The court also issued opinions on Tuesday, as it works toward the term’s conclusion at the end of June.

In Kellogg Brown & Root Services v. Carter , the court was unanimous in saying a former employee of the company who filed a whistleblower suit accusing it of defrauding the government over work performed during the war in Iraq was filed too late.

In a decision written by Justice Samuel A. Alito Jr., the justices said a law that extends the time for filing fraud claims during wartime does not apply to civil suits.

In a bankruptcy case, the disagreement among justices was more about the impact of the decision than the facts of the case.

Justice Sonia Sotomayor wrote for the majority that bankruptcy courts have authority to rule on certain related disputes if the parties to the case consent.

Chief Justice John G. Roberts Jr. was among the three dissenters, saying the decisions had to be made by judges granted their authority under Article III of the Constitution, which bankruptcy judges are not.

“The impact of today’s decision may seem limited,” Roberts wrote, but he added: “The majority’s acquiescence in the erosion of our constitutional power sets a precedent that I fear we will regret.”

Sotomayor indicated that Roberts’s response was disproportionate to the majority’s “pragmatic” decision.

“To hear the principal dissent tell it, the world will end not in fire, or ice, but in a bankruptcy court,” she wrote.

The case is Wellness International Network v. Sharif.