The Mathis removal letter recapped charges that Brewer made in a letter last week to the full commission. She accused its members of neglect of duty and misconduct by not following constitutional processes and criteria for mapping.
The commission and individual commissioners had formally responded by a Monday deadline set by Brewer.
The commission, as well as Mathis and the two Democrats individually, denied wrongdoing and said the governor's criticism undermined the commission's independence.
However, the two Republicans commissioners' separate responses provided support for Brewer's criticism. They said the commission's draft maps didn't adequately comply with the constitutionally mandated criteria for mapping. Those include equal population, minority voting rights, competition between the parties, compactness and communities of interest.
Republicans previously said the draft congressional map favored Democrats, though Republicans appeared to hold solid edges in four U.S. House districts, versus two for Democrats and three being labeled competitive.
During the Senate vote, Republican Sen. Linda Gray of Glendale said Mathis worked only with the two Democratic commissioners and engineered the award of the mapping consultants contract "under the cloud of open meeting violations and alleged bid-rigging."
Democrats said Republicans had no basis for removing Mathis other than partisan politics.
"What we have here is a witch hunt ... with a pre-determined outcome. It is a disgrace. We get it — you don't like the maps," said Sen. David Schapira, D-Tempe.
Republicans defended their action to remove Mathis, noting that the Arizona Constitution permits the governor to remove a commissioner with consent of the Senate.
"We are doing what is constitutionally correct. When we see malfeasance, we replace it," Sen. Steve Smith said.
A special House-Senate committee reported Monday that the commission's mapping process was flawed and gave short shrift to other redistricting criteria, including creating districts that are compact and that respect communities of interest.
Democratic legislators boycotted the special committee's meetings, calling it a power grab aimed at preserving GOP incumbents' seats by pressuring the commission to not emphasize creating competitive districts.
Besides holding solid majorities in both legislative chambers, Republicans now control five of the state's eight U.S. House districts, up from three before the 2010 election.
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