The Colgrove v. Battin case in 1972 was a U.S. Supreme Court decision that addressed the constitutionality of six-member juries in civil trials at federal district courts, as opposed to the traditional twelve-member jury. The plaintiffs argued that this violated their Seventh Amendment right to trial by jury, which they believed implied a requirement for twelve jurors based on historical precedent and common law tradition. However, the court ruled 5-4 against them, stating there is no constitutional mandate for a specific number of jurors in civil cases under Federal Rule of Civil Procedure 48 permitting six-person juries. The majority opinion held that what matters is not the size but whether it serves its intended function - preventing oppression by government and providing an "interposition between the accused and his accuser". Therefore, smaller juries were deemed acceptable if they could fulfill these roles effectively.

In the dissenting opinion for Colgrove v. Battin, Justice William O. Douglas argued that the majority's decision to uphold a Montana law allowing six-person juries in civil trials was inconsistent with historical precedent and violated the Seventh Amendment of the Constitution, which guarantees trial by jury in civil cases. He contended that this amendment should be interpreted as requiring a 12-member jury since it is based on English common law tradition where such size was standard. Furthermore, he expressed concern about potential erosion of individual rights if states were allowed to deviate from established federal standards without clear justification or compelling reasons. He also noted that smaller juries could lead to less reliable verdicts due to reduced diversity of viewpoints and increased influence of individual jurors' biases or prejudices.