In the case of Peretz v. United States, the Supreme Court ruled in 1990 that a defendant can consent to have a federal magistrate judge preside over jury selection during their trial. Martin Peretz was charged with importing and possessing cocaine with intent to distribute it. He agreed to have a magistrate conduct voir dire (the process of questioning prospective jurors) instead of a district court judge. After being convicted, he appealed on grounds that his rights were violated because only an Article III judge could oversee jury selection according to Federal Magistrates Act. The Supreme Court disagreed, ruling 6-3 that if defendants knowingly and voluntarily agree for magistrates to oversee this part of their trials, then no violation occurs.

In the dissenting opinion for Peretz v. United States, Justice Marshall, joined by Justice Brennan and Justice Blackmun, argued that the majority's decision to allow a magistrate judge to preside over jury selection in felony trials without explicit defendant consent was inconsistent with both the Federal Magistrates Act and constitutional principles of separation of powers. They contended that Congress did not intend for magistrates to perform such significant duties in felony cases when it enacted this legislation. The dissent also expressed concern about potential erosion of Article III protections if non-Article III judges were allowed more involvement in felony cases. Furthermore, they disagreed with the majority's assertion that defendants' rights were adequately protected through their ability to object or appeal; instead arguing these mechanisms are insufficient safeguards against potential abuses or errors by magistrate judges who lack life tenure and other Article III guarantees.