In the 1945 case of Chatwin v. United States, the Supreme Court ruled on a matter involving polygamy and cohabitation laws in Utah. The appellants were members of a religious sect that practiced polygamy, and they had been convicted under federal law for conspiracy to violate these state laws. They argued that their convictions violated their First Amendment rights to freedom of religion. However, the Supreme Court disagreed with this argument, upholding their convictions by stating that while individuals have the right to believe what they want regarding marriage and family structure as part of their religious beliefs, when those beliefs are put into action in ways that conflict with established law (in this case through practicing polygamy), it becomes an issue not protected by constitutional rights to freedom of religion.

In the dissenting opinion for CHATWIN v. UNITED STATES, Justice Murphy argued that the Mann Act was being misapplied in this case. He contended that it was not intended to be used as a tool to prosecute polygamy or bigamy, but rather to combat commercialized vice and involuntary prostitution. The majority's interpretation of "immoral purposes" within the act is too broad according to him; he believed it should only cover sexual activities performed for hire or under compulsion. Furthermore, he pointed out inconsistencies in applying federal law over state jurisdiction on matters related to marriage and domestic relations traditionally left up to states' discretion. Lastly, Justice Murphy expressed concern about potential misuse of such an expansive interpretation of the Mann Act against unconventional yet consensual relationships between adults.