The court let stand Pauline Newman's suspension from hearing cases after declining to review her challenge to the Federal Circuit's action over alleged mental unfitness.
Newman, appointed to the Federal Circuit in 1984, has argued the suspension amounts to an unconstitutional removal because only Congress can impeach or remove a federal judge.
Three independent experts found Newman mentally fit, but the suspension has continued for years after colleagues launched the inquiry following brief fainting spells.
The case centers on whether a chief judge and a panel of fellow judges can sideline a lifetime-appointed colleague indefinitely, a question critics say could affect judicial independence far beyond Newman.