In Gomez v. United States, the Supreme Court ruled that a federal magistrate judge did not have the authority to supervise jury selection in felony trials unless both parties consented. The case arose after two men were convicted of drug charges and argued their convictions should be overturned because a magistrate supervised their jury selection without their consent. The government contended that this was permissible under the Federal Magistrates Act, which allows magistrates to be assigned "additional duties." However, the Supreme Court disagreed with this interpretation of the law. It held that supervising jury selection is more than an additional duty; it's a critical stage in criminal proceedings where defendants have substantial rights at stake. Therefore, only district judges or circuit judges can oversee such process unless all parties agree otherwise.

In the dissenting opinion for Gomez v. United States, Justice White argued that there was no constitutional or statutory basis to prevent magistrate judges from supervising jury selection in felony trials. He contended that Congress had granted magistrates broad authority to perform any additional duties consistent with the Constitution and laws of the United States, which could include overseeing voir dire. Furthermore, he pointed out that district courts have always been able to delegate certain tasks to magistrates under their general administrative powers. In his view, this delegation did not infringe upon a defendant's Sixth Amendment right because it did not involve final decision-making power on issues of guilt or innocence; rather, it was an administrative function related to trial management. Therefore, he disagreed with the majority’s ruling that only Article III judges could preside over jury selection in felony cases.