In the case of New York ex rel. Halvey v. Halvey (1946), the U.S Supreme Court was tasked with determining whether a state court could modify an out-of-state child custody order without violating full faith and credit clause of the Constitution, which requires states to respect each other's laws and judicial decisions. The dispute arose when Mrs. Halvey moved from Florida to New York with her children after being granted custody in a Florida divorce decree, but Mr. Halvey subsequently obtained a modification of that decree from a New York court granting him visitation rights not provided for in the original decree. The Supreme Court ruled that while states must give "full faith and credit" to judgments issued by courts in other states, this does not mean they are bound by those judgments if their own public policy is at odds with them - particularly regarding matters such as domestic relations where local control is traditionally strong. Therefore, it held that although Mrs.Halvey had been awarded sole custody under Florida law, this did not prevent New York courts from modifying these arrangements based on its own assessment of what would be best for the children.

In the dissenting opinion for New York ex rel. Halvey v. Halvey, Justice Frankfurter argued that the Full Faith and Credit Clause of the Constitution should not be interpreted to compel states to enforce custody decrees from other states without any discretion or consideration of changed circumstances. He contended that such an interpretation would undermine state sovereignty and potentially harm children by forcing them into unsuitable living situations due to changes in circumstance since the original decree was issued. Instead, he advocated for a more flexible approach where courts could consider whether enforcing an out-of-state decree would serve justice and protect child welfare under current conditions.