Chief Justice William Rehnquist recently wrote that he would not recuse--disqualify--himself from hearing matters related to the federal government's Microsoft antitrust case just because his lawyer son, James Rehnquist, is working on a separate antitrust matter for Microsoft. So, when do members of the Supreme Court have to recuse themselves?
Whenever they want.
Reasons for disqualification are laid out in the United States Code (Title 28, Section 455), but the justices themselves are their own final arbiters. According to the statute, justices, judges, and magistrates should recuse themselves if they have a personal bias concerning anyone in the case, or independent knowledge of the facts in dispute; if they worked on the case as a private or government lawyer; or if they or close relatives have a financial interest in the case.
Since Supreme Court justices tend to be well off, and since lawyers often marry lawyers and beget more lawyers, money and family come up the most as reasons for recusal. Justice Stephen Breyer at his confirmation said he would not hear insurance cases because of his substantial holdings in Lloyds. Justice Ruth Bader Ginsburg participated in a case before realizing her husband owned stock in some of the companies involved. Ginsburg's husband divested as the statute prescribes.
In the Microsoft matter Rehnquist concluded, "[M]y son's personal and financial concerns will not be affected by our disposition of the Supreme Court's Microsoft matters." In general justices are loath to recuse themselves from cases because it opens the way for a tie. When that happens the lower court decision is affirmed by default. If Rehnquist recuses himself from a case, the senior associate, Justice John Paul Stevens, presides.
Explainer thanks Steven Lubet, professor of law at Northwestern University, Geoffrey Hazard, professor of law at the University of Pennsylvania Law School, and Andrew Kaufman of Harvard Law School.