PHOENIX — The U.S. Supreme Court could announce at its first public session of the year in October whether state lawmakers will get to redraw Arizona’s congressional lines.

The justices have agreed to discuss a bid by the Legislature to void a provision of a 2000 voter-approved measure giving power to set the lines to the Independent Redistricting Commission. That discussion will take place at a Sept. 29 closed-door conference.

A week later, according to tradition, the high court convenes on the first Monday in October. And attorney Mary O’Grady, who represents the redistricting commission, said the justices could simply decide at that time, without further discussion, to affirm or void a lower court ruling on who has authority to craft congressional districts for 2016 and beyond.

The implications of either are significant.

A ruling summarily overturning the lower court would pave the way for the Republican-controlled Legislature to redivide the state, but this time in a manner more favorable to the GOP. And that likely would alter the current 5-4 split between Democratic and Republican members of the U.S. House.

But affirming the lower court leaves the decision in the hands of the commission and leaves the lines where they are through at least the 2020 election.

And it all could turn on the question of exactly who in Arizona is the “Legislature.”

Until 2000, state lawmakers had crafted the lines for both legislative and congressional races, often resulting in districts favoring the majority party.

Then voters created a five-member commission, based on the notion it would reduce the effect of politics.

But redistricting efforts following the 2010 census, when the state gained another seat in the U.S. House, got mired in partisan political bickering, which got worse after the first congressional race after that resulted in Democrats winning five of the state’s nine seats.

Republican lawmakers sued. Their legal argument is centered on that question of legislative authority.

In legal briefs, House staff attorney Peter Gentala pointed out the Elections Clause of the U.S. Constitution says, “The times, places and manner of elections for senators and representatives shall be prescribed in each state by the Legislature thereof.” He said that means the lawmakers elected by voters — and not the commission.

But a majority of a three-judge panel which heard the case in Phoenix concluded it’s not that simple.

U.S. District Judge Murray Snow, writing for the majority, said the term “legislature” refers not to the 90 members but to the state’s entire lawmaking process.

“Since its inception, the Arizona Constitution has reserved the initiative power to its people,” Snow wrote. That includes the power of voters to make their own laws and state constitutional provisions.

In this case, the judge wrote, voters used that power to create the Independent Redistricting Commission.

Put simply, the judge said, the voters decided that, for purposes of redistricting, the commission is the legislature. And he said voters had the right to do that.

O’Grady said legal precedent is on the commission’s side. She said federal courts, looking at the Elections Clause, has never ruled that only the elected legislators are empowered to draw boundaries.