In Louisiana Ex Rel. Nelson v. Police Jury of St. Martin's Parish, the Supreme Court of the United States was asked to decide whether a state statute that authorized the Police Jury of St. Martin's Parish to levy a tax on the property of non-residents was constitutional. The Court held that the statute was unconstitutional because it violated the Privileges and Immunities Clause of the Fourteenth Amendment. The Court reasoned that the Privileges and Immunities Clause of the Fourteenth Amendment was intended to protect the rights of citizens of one state when they travel to another state. The Court held that the statute in question violated this clause because it imposed a tax on non-residents that was not imposed on residents. The Court also held that the statute violated the Equal Protection Clause of the Fourteenth Amendment because it discriminated against non-residents. The Court concluded that the statute was unconstitutional and that the Police Jury of St. Martin's Parish could not levy a tax on the property of non-residents. The Court also held that the state of Louisiana could not impose a tax on the property of non-residents that was not imposed on residents.

In the case of Louisiana Ex Rel. Nelson v. Police Jury of St. Martin's Parish, the Supreme Court was asked to decide whether a state law allowing for taxation on certain property owned by churches violated the Fourteenth Amendment’s Equal Protection Clause and Establishment Clause. The majority opinion held that it did not violate either clause because there was no evidence that any church had been singled out or treated differently than other organizations in similar circumstances, nor did it constitute an establishment of religion as prohibited by the First Amendment since its purpose was to raise revenue rather than promote religious beliefs or practices. The dissenting opinion argued that while there may have been no direct discrimination against churches, they were still being unfairly targeted due to their unique status as non-profit entities exempt from most taxes under state law; thus, this tax constituted an indirect violation of both clauses since it effectively imposed a burden on them without providing equal protection or establishing religion in any way. Furthermore, even if such taxation could be justified based on some compelling interest related to public welfare (e.g., raising revenue), then all similarly situated organizations should also be subject to such taxes regardless of their religious affiliation—which is not what happened here according