The U.S. Supreme Court case Whitney National Bank in Jefferson Parish v. Bank of New Orleans & Trust Co., et al., 1964, revolved around the issue of whether or not a national bank could establish branches in locations where state banks were prohibited from doing so by state law. The Whitney National Bank had established two new branches within Jefferson Parish, Louisiana without obtaining approval from the Comptroller of Currency as required by federal law and contrary to Louisiana's state laws which restricted branch banking. The Bank of New Orleans filed suit against Whitney arguing that it was operating illegally. In its decision, the Supreme Court ruled in favor of the Bank of New Orleans stating that while national banks are governed primarily by federal statutes, they must also respect and adhere to relevant state laws regarding branch banking operations unless those laws directly conflict with federal legislation.

In the dissenting opinion for Whitney National Bank in Jefferson Parish v. Bank of New Orleans & Trust Co., Justice Harlan argued that the majority's decision was inconsistent with previous rulings and could potentially disrupt banking practices across the country. He contended that there was no clear evidence to suggest that Congress intended to prohibit national banks from establishing branches through mergers, as long as they complied with state laws. Furthermore, he pointed out that this interpretation had been accepted by federal regulatory agencies for many years without any significant problems arising. Therefore, he believed it would be more appropriate to defer to their expertise rather than imposing a new interpretation based on an ambiguous statutory provision. Finally, Justice Harlan warned against judicial activism and urged his colleagues not to overstep their authority by making policy decisions better left to lawmakers or regulators.