Jan 27 (Reuters) - A recent decision by the U.S. Supreme Court that dealt with a narrow issue in a redistricting case from Texas suggests that the nation's top court is ready to reconsider a key part of the Voting Rights Act, a major piece of civil rights legislation.

In the Jan. 20 decision, which tossed a Texas electoral map back to a lower court, the Supreme Court made a reference to "serious constitutional questions" raised by the act, which was passed in 1965.

Legal experts have identified an Alabama case working its way through the courts as a vehicle through which the Supreme Court could eventually take another look at the act.

Section 5 of the Voting Rights Act requires that states with a history of voting rights violations, typically those in the South, get approval from either the Justice Department or a three-judge federal court in the District of Columbia before changing their election rules.

Several states have challenged Section 5 over the years on the grounds that it interferes with their right to govern elections under the powers reserved to them by the 10th Amendment. To date, the Supreme Court has rejected those challenges.

The constitutionality of the voting rights laws were not at issue in the Texas case, as Chief Justice John Roberts made clear in oral arguments on Jan. 9. But the court's decision on Jan. 20 seemed to signal it was ready to consider the issue.

In that decision, which was unanimous, the Supreme Court referred back to language it used in a 2009 case, where it found that "intrusions on state sovereignty" brought by Section 5 raised "serious constitutional questions."

And, in a concurring opinion, Justice Clarence Thomas restated his position in the 2009 case. "The extensive pattern of discrimination that led the Court to previously uphold [Section 5] as enforcing the 15th Amendment no longer exists," Thomas wrote.

The Supreme Court's decision on Jan. 20 shows that the constitutionality of the Voting Rights Act, and Section 5 in particular, is "on the court's mind," said Bert Rein, an attorney for Shelby County, Alabama, which is currently challenging the constitutionality of Section 5.

A lower court ruled against the Alabama county, and the Court of Appeals for the District of Columbia Circuit heard oral arguments in the county's appeal on Jan. 19.

"Whatever the ruling is, I think the losing party will seek certification from the Supreme Court," said Deborah Archer, a law professor and Director of the Racial Justice Project at the New York Law School, which filed an amicus brief in support of the U.S. government position in the Alabama case.

Legal experts said the Alabama case may be ripe for consideration by the Supreme Court, after the appeals court rules. A decision by the appeals court could take several months.

Richard Pildes, a professor at New York University Law School who specializes in election law, said that if the appeals court finds Section 5 to be unconstitutional, "the Supreme Court would certainly hear the case on the merits."

The Supreme Court had the opportunity to rule on the constitutionality of Section 5 in the 2009 case, Northwest Austin Municipal District No. 1 v Holder, a challenge by a small district in Texas.

"Everyone thought the Supreme Court would take on the constitutionality question two years ago," said Debo Adegbile, Litigation Director at the NAACP-Legal Defense Fund, who argued the 2009 case in support of the Voting Rights Act.

The majority of the court instead chose to sidestep the constitutional issue and decided the case on narrow statutory grounds. Only Justice Thomas, in a separate opinion, said he would have ruled that Section 5 of the Act was unconstitutional.

If the Alabama case reaches the Supreme Court, the justices will have to face the constitutional question head on, since it is the only legal issue in the case.

The first challenge to the constitutionality of the Voting Rights Act was brought by South Carolina. In a 1966 case called South Carolina v Katzebach, the Supreme Court ruled that the legislation was constitutional.

Since then, Congress has reauthorized the Act four times, and legal challenges have been brought each time. The Supreme Court upheld the constitutionality of the Act again in 1973, 1980, and 1999. It has not yet ruled on the constitutional challenges that have been raised since the 2006 reauthorization.

The Alabama case is Shelby County, Alabama v Holder, U.S. Appeals Court, District of Columbia, no. 11-5256

The Texas case is Perry v Perez, U.S. Supreme Court, no. 11-713

(Reporting by Rebecca Hamilton)

Follow us on Twitter: @ReutersLegal