In the Williams v. Florida case of 1969, the United States Supreme Court ruled that a six-member jury in state criminal trials was constitutional. The defendant, Johnny Williams Jr., had been convicted by a six-person jury in Florida and argued that this violated his Sixth Amendment right to trial by an impartial jury as it did not explicitly specify the number of jurors required for a fair trial. However, the court held that "trial by jury" referred to quality rather than quantity and focused on whether or not justice was done rather than how many people decided on it. Therefore, having fewer than twelve members did not necessarily make a jury less effective or violate any rights provided under the Constitution's Sixth Amendment.

In the dissenting opinion for Williams v. Florida, Justice Hugo Black argued that a six-person jury was not equivalent to a twelve-person jury as required by the Sixth Amendment of the Constitution. He contended that history and tradition had established this number as an essential element of trial by jury, and any deviation from it undermined defendants' rights. Furthermore, he believed that smaller juries were more likely to make mistakes or be influenced by improper considerations due to their lack of diversity in viewpoints compared with larger juries. Thus, according to Justice Black's interpretation of the Constitution, states should not have been allowed flexibility in determining how many jurors are necessary for criminal trials.