RALEIGH, N.C. (AP) — North Carolina Republican legislative leaders on Monday opposed a plan by federal judges to use an outside expert to help them examine and possibly redraw General Assembly district lines, arguing that it's premature to hire one and questioning the expert's impartiality.

An attorney for GOP mapmakers objected to the judicial panel's intentions — announced last week — to appoint a Stanford University law school professor as what's called a "special master."

The same three judges last year struck down nearly 30 districts originally drawn in 2011 by the GOP-controlled legislature, determining they unlawfully relied too heavily on race. The General Assembly approved new lines in August, but the judges wrote last week they remained concerned that seven House and two Senate districts "either fail to remedy the identified constitutional violation or are otherwise legally unacceptable."

The judges shouldn't appoint a special master — Stanford's Nathaniel Persily or anyone else — until they issue a ruling that explains why the nine districts fall short legally and give the General Assembly another crack at rectifying problems, GOP lawyer Phil Strach wrote.

New districts are supposed to be used in the 2018 elections, and with candidate filing to begin in February there's sufficient time for the state to fix any problems, Strach added.

"The legislative defendants are concerned that the appointment of a special master as described by the court will instead affirmatively obstruct the state's ability to exercise its sovereign right to redistrict in the first instance," he wrote.

Persily has assisted judges in drawing districts in four other states.

On Monday, Strach raised flags about Persily, saying that the professor had connections to both the chief lawyer for the voters who sued over the maps, as well as to the voters' allies. For example, Strach pointed to a 2006 redistricting conference by the University of North Carolina Center for Civil Rights in which a document listed him as a conference presenter. Anita Earls, the plaintiffs' lawyer, worked for the center at the time, the paper said.

Strach also pointed to Persily's quotes in media stories about redistricting and voting laws in North Carolina and other states. Strach wrote that those stories in part exhibit "examples of possible bias" that the defendants should be allowed to ask Persily about in a court setting.

"Persily has many media appearances and published works relating to North Carolina redistricting which raise questions about his ability to fairly assess the plans before the court," Strach wrote.

Persily filed an affidavit late last week stating he knew of no grounds that disqualified him from serving as a special master in the case.

Earls and other lawyers representing the voters who originally sued over the 2011 maps hadn't filed any objections as of late Monday. Earls, who is now working for the Southern Coalition for Social Justice, said in a release last week that it had "been shown time and again that the state legislature refuses to draw fair districts that comply with the law."

The 2011 districts helped Republicans expand and retain veto-proof majorities, contributing to their ability to push a conservative agenda through state government. Further adjustments to the districts approved in August could help improve the Democrats' chances to end these supermajorities.