WASHINGTON — Retired Supreme Court Justice Sandra Day O'Connor continues to hear cases in U.S. appeals courts, while also playing a role in public policy issues. Her critics say she should do one or the other, but not both.

O'Connor, 81, was forced to apologize for 50,000 recorded telephone calls made to Nevada voters in which she supported a ballot measure to change the way state judges are selected. O'Connor said she did not authorize the calls featuring her recorded voice, much less their post-midnight delivery. But she also defended her involvement in the campaign that included her appearance in a television commercial.

In September, federal judges in Iowa stayed away from a conference on judicial elections at which O'Connor spoke in the midst of another campaign over ballot issues. The judges had received an informal opinion that their presence would violate the judiciary's ethics code.

Most recently, O'Connor hosted an after-hours reception at the court that was billed as a celebration of Bristol Bay in Alaska. But the featured speakers, other than O'Connor, were opponents of a proposed Alaskan copper and gold mine. They were in Washington to lobby lawmakers and regulators against the proposed Pebble Mine.

Arthur Hellman, an ethics expert at the University of Pittsburgh law school, said O'Connor should consider stopping her participation in court cases if she "wants to engage in this level of political or politically related activity."

Partisan-tinged questioning of conduct by high court justices has grown.

Liberal interest groups have faulted Justices Antonin Scalia and Clarence Thomas for speaking at a private dinner hosted by Charles Koch, one of two energy-company-owning brothers who, liberal groups say, have too much sway on policymakers.

Some liberals have called on Thomas to sit out the expected high court fight over the health care law because of his wife's public criticism of the law. Some conservatives say Justice Elena Kagan should not take part in the health care case because of her work in the Obama administration before joining the court.

O'Connor has traveled the country since her retirement in 2006 to criticize costly election campaigns for state judges, promote enhanced civics education for schoolchildren and advocate for Alzheimer's research. Her husband, John, died in 2009 of complications from Alzheimer's disease.

Her primary focus has been on judicial independence, which she believes is harmed by electing judges.

At the same time, she has heard cases on appeal since her retirement. It is not uncommon for retired justices to sit with federal appeals courts from time to time. Justice David Souter, who left the court in 2009, has heard cases with the Boston-based court.

Through the end of March, O'Connor had written two appellate decisions and joined the majority in a half-dozen others this year. None of the cases involved judicial elections or the fate of the Alaska bay.

The continuing judicial work allows O'Connor, who earns $213,900, to receive salary increases that are tied to inflation. Judges who stop hearing cases receive a pension equal to their final annual salary as a full-time judge, but are excluded from subsequent cost-of-living increases.

Last week, O'Connor was the host of a Supreme Court reception "to celebrate the economic, cultural and ecological values of Alaska's Bristol Bay Watershed."

Opponents of the proposed huge mine near the bay fear it will devastate the world's largest wild sockeye salmon fishery. The Environmental Protection Agency recently said it would study potential effects from the mine. EPA Administrator Lisa Jackson attended and briefly spoke at the reception.

O'Connor declined to answer questions for this story. But the head of the Wild Salmon Center, lead sponsor of the event, said O'Connor's participation came about because of their friendship and her love of fly fishing.

Guido Rahr, the center's president, said his group hasn't taken a position on the mine and that the speakers were careful to "make sure we were respecting the location" of the reception at the court.

Rahr said participants mainly "ate yummy salmon treats" and looked at National Geographic photos of the bay.

But one speaker was a former Alaska state Senate president, Rick Halford, who told reporters the next day that the proposal was a "very, very dangerous kind of mine."

Supporters of the project made their own visit to Washington a couple of weeks earlier. They were not received at the high court.

Hellman, the Pittsburgh ethics expert, said he finds the court reception particularly troubling because "we're talking about political activity. It's a lobbying effort and she is lending her considerable prestige to that effort."

Another ethics professor, Stephen Gillers of New York University, said that if the speeches were not about advocacy, then the event itself probably does not pose an ethical problem for O'Connor. On the other hand, Gillers said it is possible O'Connor would have to step aside from any appellate case involving the groups that sponsored the reception.

The court hosts 50 to 60 after-hours events a year, many related to the court. Guidelines for use of the building forbid partisan political activity and fundraising, and require a justice to sponsor an event. A cash bar and dancing are not permitted.

Supreme Court justices are not covered by the ethics rules that apply to all federal judges. Still, justices generally adhere to those rules, Hellman said.

O'Connor's involvement in last year's ballot issues in Iowa and Nevada also drew a rare rebuke from another federal judge.

Senior Judge Laurence Silberman of the federal appeals court in Washington, D.C., said "the issue of whether state court judges should be chosen or ratified by election or solely by appointment is a political issue on which serving federal judges should not publicly advocate, one way or the other."

Silberman said that unlike the criticism of Scalia and Thomas, which he termed phony issues, O'Connor's advocacy "is a real ethical issue."

O'Connor took part in a conference in Des Moines, Iowa, in September on the topic of judicial elections. That appearance came during a contentious campaign about whether voters should retain three Iowa Supreme Court justices who were part of a unanimous court ruling in favor of gay marriage.

Federal judges in Iowa had been invited to attend by the Iowa State Bar Association, according to Chief Judge Robert Pratt of the Southern District of Iowa

But Pratt wondered whether their attendance would be improper.

Lacking the time for a formal opinion from the judiciary's ethics committee, the judge took advantage of a less formal process and called an ethics committee member for his views.

Pratt said the committee member, U.S. District Judge Richard Kopf, informally advised the judges to stay away.

They did, but O'Connor attended and said voters shouldn't punish judges when they disagree with their decisions. In the end, the three justices were ousted.