PHOENIX - Members of the Independent Redistricting Commission do not need to answer certain questions from those who are suing them, a federal court has ruled.

The judges accepted the argument by commission attorneys that its members are entitled to the same immunity from having to explain their decisions as state legislators. That allows them to rebuff inquiries from those who are suing them.

But the judges hearing the case set for trial next month cautioned the commissioners that they may want to think twice before asserting that privilege. They ruled any claim of privilege is an all-or-nothing prospect.

The ruling - and the warning - could ultimately affect the outcome of the case.

Challengers contend that at least some of the five commissioners had improper and illegal motives in how they drew the lines for the state's 30 legislative districts.

The court's decision, in essence, means that if commissioners seeking to rebut those allegations claim the privilege, they cannot decide halfway through the case they now want to explain their personal reasons for making those decisions.

The outcome of the trial is significant because if the judges find the commissioners acted improperly, they likely would order them to totally redraw the map for the 2014 election, a move that could alter political balance in the state.

Voters created the commission in 2000 to redraw legislative and congressional district lines after the census every 10 years, taking that task away from state lawmakers. Proponents said the change would make the process and the outcome less political.

A lawsuit filed last year in U.S. District Court contends the commission broke the law when it created districts with varying populations despite state and federal laws generally requiring all voting districts to have approximately the same number of people. The commission's maps have a difference of more than 8 percent between the most and least-populated districts.

Commission attorney Mary O'Grady does not dispute the numbers. But she argues that there are legitimate reasons for the differences, like having to comply with the federal Voting Rights Act, which precludes states from diluting minority voting strength, and meeting a voter-mandated requirement to create as many politically competitive districts as possible.

But attorney David Cantelme called those claims little more than a cover for the real motive for the population differences: to give Democrats an unfair edge.

And that's where the question of the motives of the commissioners - and their ability to be questioned about them - comes in.

Cantelme said the evidence will show the commission pushed as many Republicans as possible into Republican-dominated districts to leave as many districts as possible safe for Democrats. He said the commission did that by overpopulating GOP districts and underpopulating the Democratic ones.

One example, he said, is District 8, which runs from Oracle and San Manuel through Coolidge and Florence into the San Tan Valley and up through Globe. Democrats have a 10-point registration edge over Republicans.

Cantelme said that was accomplished by creating a district with 208,422 residents. If each district were equal in population, the figure would be closer to 213,000.

Beyond the population differential, Cantelme contends the lines were drawn in a way to remove as many Republicans from the district as possible. Without that shift, he said it would have been a politically competitive district.

The actual results of the 2012 election, however, suggest that if the commission were trying to create a Democrat-leaning district, it failed.

Both House members elected from the district, Thomas Shope of Coolidge and Frank Pratt of Casa Grande, are Republicans. Democrat Barbara McGuire of Kearny was elected to the Senate.

The three-judge panel hearing the case wants the trial to start next month. Judge Roslyn Silver said she wants there to be enough time to redraw the lines - a year-long process last time - if the current ones are found legally invalid.