Retired Supreme Court Justice Sandra Day O'Connor is apologizing for the 50,000 recorded telephone calls made to Nevada voters in which she supports a ballot measure to change the way state judges are selected.

O'Connor said Wednesday that she did not authorize the use of her recorded statement in the robo calls, which awakened many Nevadans after midnight Monday. The calls were supposed to be made midday.

But O'Connor said that, whatever the time, her voice should not have been used at all.

"I did not authorize the use of my recorded statement as part of automated telephone calls to Nevada residents, and I regret that the statement was used in this way," she said in a statement issued through the Supreme Court.

At the same time, she defended her involvement in the campaign to amend the state constitution to reduce the role of elections in the choice of judges. O'Connor has appeared in a television commercial on behalf of the Question 1 measure that Nevadans will vote on on Tuesday.

Some critics have said O'Connor, the first woman on the Supreme Court, should refrain from political activity because she continues to hear cases as a federal judge. On Tuesday, she was in the majority on a panel of federal appeals court judges that struck down a key part of an Arizona law requiring voters to prove they are citizens before registering to vote.

O'Connor, 80, has traveled the country to criticize costly election campaigns for judges. She has said judicial elections erode confidence in an impartial judiciary and feed the perception that justice is for sale.

Since her retirement in 2006, O'Connor has been active on other issues as well, including calling for enhanced civics education for schoolchildren and advocating for Alzheimer's research. Her husband, John, died last year of complications arising from Alzheimer's disease.