Trial will begin Monday in federal court in Phoenix on a lawsuit by Republicans challenging legislative redistricting in Arizona.

The lawsuit claims that the Arizona Independent Redistricting Commission drew the boundaries to favor Democrats. The final vote on the redistricting map was 3-2, with two Democrats and the commission's independent chairwoman voting in favor and the two Re[ublican members voting against.

A last-minute filing in the case shows GOP lawyers claim to have new evidence to back up their case. The filing says they want to call an unscheduled witness.

The fundamental claims in the case is that the commission unevenly split populations among legislative districts in an effort to get more Democrats elected.

Lawyers for the commission have said the group was striving to meet requirements of the Voting Rights Act and the state Constitution, which mandates five equal but competing requirements for redistricting.

The boundaries drawn by the commission were used in last year's elections and led to Republican control of both legislative chambers, 17-13 in the Senate and 36-24 in the House. Those numbers were down from 21-9 and 40-20 in favor of Republicans in the previous two-year election cycle.

Republicans also have sued the commission over congressional redistricting, and that case is being handled separately. Arizona added a ninth congressional district last year, and Democrats won five seats. In the previous election cycle, Republicans held a 5-3 edge in state congressional seats.