PHOENIX - Members of the Independent Redistricting Commission want a federal court to block them from being questioned about the legislative maps they drew.

In legal papers filed in U.S. District Court, attorneys for the five commissioners said their actions are protected by "legislative privilege," a legal concept that generally prevents lawmakers from being questioned or sued about how they reached a decision. And they want a three-judge panel hearing the case to preclude lawyers for the challengers from being allowed to ask them about it in pretrial depositions.

But Joe Kanefield, one of the commission's attorneys, said this is just the first step toward asking the federal judges to bar challengers from putting commissioners on the stand at trial to get them to explain why they did what they did.

There is a long line of cases saying some actions of legislators are off-limits to outside questioning. And there already have been court rulings affirming commissioners, in drafting the maps, are acting in a legislative capacity.

But there also are other rulings that back the contention not everything the commissioners did can be considered a legislative action. Actions that were strictly administrative can be subject to legal scrutiny.

Hanging in the balance is whether the court will overturn the lines the commission drew for the state's 30 legislative districts, which were used in last month's election. That election resulted in Democrats picking up four seats in both the state House and the Senate.

The lawsuit contends commissioners acted deliberately to make that happen.

Voters created the commission in 2000 to draw both legislative and congressional boundaries, taking the task away from the Legislature itself. The constitutional provision sets standards for the commission to use, from ensuring compliance with federal voting laws to protecting communities of interest and, when possible, creating competitive districts.

It also says districts are supposed to have equal population. Using figures from the 2010 census, that should come out to about 213,000 in each of the 30 districts. The commission's own data show it created districts ranging from 203,026 to 220,157 people.

The legal claim, however, goes beyond pure numbers.

Challengers contend commissioners purposely moved registered Republicans out of what would have been otherwise competitive districts and instead "packed" them into adjoining districts where Republicans already had an edge. That, the lawsuit contends, resulted in deliberately underpopulated districts where Democrats had a better chance of winning.

Mary O'Grady, another commission attorney, has argued that there were legitimate reasons for those changes, including protecting minority voting strength as required by federal law.

It will be up to the three-judge panel to decide whether that population variation is legal. If the judges rule the process was flawed, they could order the commission to start over again and draw new lines for the 2014 race, this time following different procedures.

This fight relates to a bid by challengers, in preparing for the trial, seeking to question commissioners ahead of time on a host of issues they believe will help buttress their claims that the changes were made for illegitimate reasons.

For example, they want to explore how the two Republicans and two Democrats, chosen by legislative leaders, then selected Tucsonan Colleen Mathis, a registered political independent, to chair the panel. There are allegations Mathis was really a Democratic sympathizer as her husband, Christopher, had worked to elect Democratic lawmakers.

The challengers also want to inquire about who was hired for legal counsel and mapping consultant or whether the commissioners gave any consideration to objections to the map filed by the Republican-controlled Legislature.

Kanefield said how commissioners made their decision is not subject to outside questioning, any more than lawmakers can be questioned in court about why they voted for a specific measure.

Where it could be a closer call is his contention that they also cannot be asked about conversations they had with the consultants, including the one hired to craft the final map. And Kanefield even wants the court to preclude questioning about who they hired to draw the map in the first place.

"That is part of the commission's legislative process," he said, saying selecting a mapmaker is "integral" to the legislative duties of drawing the lines.

The state Court of Appeals, however, looking at a related issue, rejected the commission's contention that the conversations commissioners had about hiring a mapping consultant are protected by legislative privilege. Judge Donn Kessler said while the decision of whom to hire relates to the legislative decisions the commission makes, these are discretionary decisions and not policymaking decisions that are entitled to legislative immunity.

Kanefield noted, though, that the federal court is not legally required to accept the ruling of the state appellate court.

Commission lawyers also want to block questioning of Christopher Mathis, calling that "an end run about legislative privilege and an attempt to annoy, embarrass and oppress the Mathises." Anyway, they said, the law prevents one spouse from being questioned about communications with the other during their marriage.